"user-defined exceptions be derived from Exception". It is only a recommendation in the sense that you can use arbitrary classic classes. If the rule is eventually tightened, it is ok if new-style classes are not allowed as exceptions right now. An action is only needed if you pronounce that it is desirable to allow new-style classes as exceptions - which would necessarily have a base class that is not derived from Exception.
Well, in the long run I would like all classes to be new-style classes, so at that point at the latest, exceptions will have to follow. Long before that moment, I would like to encourage people to use new-style classes for everything, and that should include exceptions. (Also, at some point before the end state, the default for a class statement would become to create a new-style class rather than a classic class.)
This is somewhat separate from enforcing the "exceptions must derive from Exception" rule. We should start warning about string exceptions as well as about class exceptions not deriving from Exception soon. Whether Exception should become a new-style class before, after or at the same time as full enforcement of that rule is an open issue.
(Barry, are you taking notes for the transition-to-all-exceptions- deriving-from-Exception PEP?)
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)