It's for times like this that I wonder if a simple serialization protocol might be worth it--something separate from __str__() but much simpler than the pickle protocol.  __str__() could be the fallback.  In the end, though, I always conclude that it's not worth adding yet another optional protocol to objects.  Still, it would help in this case (at least for anything that knows to make use of the simple serialization protocol).

Alternately, would it make sense to add special handling of enums to the json module?  Do we already with pickle?