Hash is already handled, but String and Array are not (and perhaps other classes that map to YAML core types). In my system I have subclasses for Hash, String, and Array, so those are the ones I've played with so far.
The two tests below each mirror the ones that are in test_hash.rb. They can probably be copied to all of the other test files, or perhaps made into a mixin for all of the tests.
Failing test_string.rb and test_array.rb patch: https://gist.github.com/1482427
This is fixed in 59ecddb and e2fcf9a
@tenderlove It seems that this patch broke Strings that have actual values. Note that Array works as expected. See the following gist:
ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin11.3.0]
@jrafanie should be fixed in 620fc6d