I have a fairly strong aversion to the way they implemented enum for ActiveRecord - choosing to back it with ints and also leaking that implementation detail through using the ordering of the enums as the int is a bad choice. Also the method name collision issues that go along with that are just silly - it would be so much easier to just prefix the methods with the column name, e.g. #status_new?
There's some other interesting stuff in there, though, and this is a good writeup of some interesting features.