diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 7d2ed7538da45..f86a3b21fbd19 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,15 @@
 *Edge*
 
+* Disable the Accept header by default [Michael Koziarski]
+
+    The accept header is poorly implemented by browsers and causes strange
+	errors when used on public sites where crawlers make requests too.  You
+	should use formatted urls (e.g. /people/1.xml) to support API clients.
+
+	Alternatively to re-enable it you need to set:
+
+	config.action_controller.use_accept_header = true
+
 * Do not stat template files in production mode before rendering. You will no longer be able to modify templates in production mode without restarting the server [Josh Peek]
 
 * Deprecated TemplateHandler line offset [Josh Peek]
diff --git a/actionpack/lib/action_controller/base.rb b/actionpack/lib/action_controller/base.rb
index 58eb5cabcd03c..c28e9005cfde2 100755
--- a/actionpack/lib/action_controller/base.rb
+++ b/actionpack/lib/action_controller/base.rb
@@ -340,6 +340,16 @@ class Base
     cattr_accessor :optimise_named_routes
     self.optimise_named_routes = true
 
+    # Indicates whether the response format should be determined by examining the Accept HTTP header,
+    # or by using the simpler params + ajax rules.
+    #
+    # If this is set to +true+ then +respond_to+ and +Request#format+ will take the Accept header into
+    # account.  If it is set to false (the default) then the request format will be determined solely
+    # by examining params[:format].  If params format is missing, the format will be either HTML or
+    # Javascript depending on whether the request is an AJAX request.
+    cattr_accessor :use_accept_header
+    self.use_accept_header = false
+
     # Controls whether request forgergy protection is turned on or not. Turned off by default only in test mode.
     class_inheritable_accessor :allow_forgery_protection
     self.allow_forgery_protection = true
diff --git a/actionpack/lib/action_controller/caching/actions.rb b/actionpack/lib/action_controller/caching/actions.rb
index 234ef8ae5b600..f3535f8330b12 100644
--- a/actionpack/lib/action_controller/caching/actions.rb
+++ b/actionpack/lib/action_controller/caching/actions.rb
@@ -166,10 +166,7 @@ def extract_extension(request)
 
             # If there's no extension in the path, check request.format
             if extension.nil?
-              extension = request.format.to_sym.to_s
-              if extension=='all'
-                extension = nil
-              end
+              extension = request.cache_format
             end
             extension
           end
diff --git a/actionpack/lib/action_controller/mime_responds.rb b/actionpack/lib/action_controller/mime_responds.rb
index 1dbd8b9e6f306..29294476f7241 100644
--- a/actionpack/lib/action_controller/mime_responds.rb
+++ b/actionpack/lib/action_controller/mime_responds.rb
@@ -114,7 +114,11 @@ def initialize(controller)
         @request    = controller.request
         @response   = controller.response
 
-        @mime_type_priority = Array(Mime::Type.lookup_by_extension(@request.parameters[:format]) || @request.accepts)
+        if ActionController::Base.use_accept_header
+          @mime_type_priority = Array(Mime::Type.lookup_by_extension(@request.parameters[:format]) || @request.accepts)
+        else
+          @mime_type_priority = [@request.format]
+        end
 
         @order     = []
         @responses = {}
diff --git a/actionpack/lib/action_controller/request.rb b/actionpack/lib/action_controller/request.rb
index c91a3387a073b..c76a93f7a109d 100755
--- a/actionpack/lib/action_controller/request.rb
+++ b/actionpack/lib/action_controller/request.rb
@@ -89,14 +89,23 @@ def accepts
         end
     end
 
-    # Returns the Mime type for the format used in the request. If there is no format available, the first of the 
-    # accept types will be used. Examples:
+    # Returns the Mime type for the format used in the request.
     #
     #   GET /posts/5.xml   | request.format => Mime::XML
     #   GET /posts/5.xhtml | request.format => Mime::HTML
-    #   GET /posts/5       | request.format => request.accepts.first (usually Mime::HTML for browsers)
+    #   GET /posts/5       | request.format => Mime::HTML or MIME::JS, or request.accepts.first depending on the value of <tt>ActionController::Base.use_accept_header</tt>
     def format
-      @format ||= parameters[:format] ? Mime::Type.lookup_by_extension(parameters[:format]) : accepts.first
+      @format ||= begin
+        if parameters[:format]
+          Mime::Type.lookup_by_extension(parameters[:format])
+        elsif ActionController::Base.use_accept_header
+          accepts.first
+        elsif xhr?
+          Mime::Type.lookup_by_extension("js")
+        else
+          Mime::Type.lookup_by_extension("html")
+        end
+      end
     end
     
     
@@ -116,19 +125,26 @@ def format=(extension)
       @format = Mime::Type.lookup_by_extension(parameters[:format])
     end
 
+    # Returns a symbolized version of the <tt>:format</tt> parameter of the request.
+    # If no format is given it returns <tt>:js</tt>for AJAX requests and <tt>:html</tt>
+    # otherwise.
     def template_format
       parameter_format = parameters[:format]
 
-      case
-      when parameter_format.blank? && !xhr?
-        :html
-      when parameter_format.blank? && xhr?
+      if parameter_format
+        parameter_format.to_sym
+      elsif xhr?
         :js
       else
-        parameter_format.to_sym
+        :html
       end
     end
 
+    def cache_format
+      parameter_format = parameters[:format]
+      parameter_format && parameter_format.to_sym
+    end
+
     # Returns true if the request's "X-Requested-With" header contains
     # "XMLHttpRequest". (The Prototype Javascript library sends this header with
     # every Ajax request.)
diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 92501133a66b4..66892fdabfd19 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -256,13 +256,9 @@ def file_public?(template_path)#:nodoc:
       template_path.split('/').last[0,1] != '_'
     end
 
-    # Returns a symbolized version of the <tt>:format</tt> parameter of the request,
-    # or <tt>:html</tt> by default.
-    #
-    # EXCEPTION: If the <tt>:format</tt> parameter is not set, the Accept header will be examined for
-    # whether it contains the JavaScript mime type as its first priority. If that's the case,
-    # it will be used. This ensures that Ajax applications can use the same URL to support both
-    # JavaScript and non-JavaScript users.
+    # The format to be used when choosing between multiple templates with
+    # the same name but differing formats.  See +Request#template_format+
+    # for more details.
     def template_format
       return @template_format if @template_format
 
diff --git a/actionpack/test/controller/caching_test.rb b/actionpack/test/controller/caching_test.rb
index d8a3ccb35bbb2..7aa4e0cd93396 100644
--- a/actionpack/test/controller/caching_test.rb
+++ b/actionpack/test/controller/caching_test.rb
@@ -131,8 +131,7 @@ def test_should_cache_ok_at_custom_path
   end
 
   def test_page_caching_conditional_options
-    @request.env['HTTP_ACCEPT'] = 'application/json'
-    get :ok
+    get :ok, :format=>'json'
     assert_page_not_cached :ok
   end
 
@@ -219,6 +218,7 @@ def request
     Object.new.instance_eval(<<-EVAL)
       def path; '#{@mock_path}' end
       def format; 'all' end
+      def cache_format; nil end
       self
     EVAL
   end
@@ -414,12 +414,6 @@ def test_xml_version_of_resource_is_treated_as_different_cache
       assert_equal 'application/xml', @response.content_type
       reset!
 
-      @request.env['HTTP_ACCEPT'] = "application/xml"
-      get :index
-      assert_equal cached_time, @response.body
-      assert_equal 'application/xml', @response.content_type
-      reset!
-
       get :expire_xml
       reset!
 
diff --git a/actionpack/test/controller/content_type_test.rb b/actionpack/test/controller/content_type_test.rb
index 2019b4a2d0ae4..8f55974172b04 100644
--- a/actionpack/test/controller/content_type_test.rb
+++ b/actionpack/test/controller/content_type_test.rb
@@ -114,6 +114,20 @@ def test_change_for_rxml
     assert_equal Mime::HTML, @response.content_type
     assert_equal "utf-8", @response.charset
   end
+end
+
+class AcceptBasedContentTypeTest < ActionController::TestCase
+
+  tests ContentTypeController
+
+  def setup
+    ActionController::Base.use_accept_header = true
+  end
+
+  def tear_down
+    ActionController::Base.use_accept_header = false
+  end
+
 
   def test_render_default_content_types_for_respond_to
     @request.env["HTTP_ACCEPT"] = Mime::HTML.to_s
diff --git a/actionpack/test/controller/mime_responds_test.rb b/actionpack/test/controller/mime_responds_test.rb
index fb2519563db13..17f5e27232222 100644
--- a/actionpack/test/controller/mime_responds_test.rb
+++ b/actionpack/test/controller/mime_responds_test.rb
@@ -166,6 +166,7 @@ def set_layout
 
 class MimeControllerTest < Test::Unit::TestCase
   def setup
+    ActionController::Base.use_accept_header = true
     @request    = ActionController::TestRequest.new
     @response   = ActionController::TestResponse.new
 
@@ -173,6 +174,10 @@ def setup
     @request.host = "www.example.com"
   end
 
+  def teardown
+    ActionController::Base.use_accept_header = false
+  end
+
   def test_html
     @request.env["HTTP_ACCEPT"] = "text/html"
     get :js_or_html
diff --git a/actionpack/test/controller/request_test.rb b/actionpack/test/controller/request_test.rb
index 20f3fd4d7b443..932c0e21a195d 100644
--- a/actionpack/test/controller/request_test.rb
+++ b/actionpack/test/controller/request_test.rb
@@ -386,7 +386,7 @@ def test_txt_format
 
   def test_nil_format
     @request.instance_eval { @parameters = { :format => nil } }
-    @request.env["HTTP_ACCEPT"] = "text/javascript"
+    @request.env["HTTP_X_REQUESTED_WITH"] = "XMLHttpRequest"
     assert_equal Mime::JS, @request.format
   end