This pull request adds auto incremented id for MongoMapper documents. According http://groups.google.com/group/mongomapper/browse_thread/thread/ecf1ab92d9ad6f11/115b72f2a6e44d29#115b72f2a6e44d29 and https://github.com/phstc/mongomapper_id2
This pull request includes only auto_incremented id, the base62 capabilities I will send in another pull request
Adding https://github.com/phstc/mongomapper_id2 capabilities
Adding to_base62 from https://github.com/phstc/mongomapper_id2
This kind of functionality is better as a plugin as not everyone will need it.
About Base62 I totally agree. But with auto incremented ID, I think that it's good for MongoMapper. It's a optional feature "auto_increment!" IMHO