Re-blessing objects is not cool nor evil. It's stupid. It's just asking for trouble, even when you know what you're doing. Why bother at all with "OO" if you're going to break the rules?

Ive done this quite a few times. I dont think its so bad depending on the purpose and requirements. For instance, I have a routine that returns a list of objects from a query that can perform a particular function. In fact the internals of those objects are quite complicated and expensive to fetch and more often than not I dont need to use all of the returned objects (but wont know if I do until too late), so I actually use two classes of objects. The first class has as its contents the required information to complete the building process. All of the accessor methods simply cause the object to complete the build, rebless, and then recall whatever it was that was originally called. That way I only need to do a full build on the objects I actually use. As a way of transparently encapsulating such behaviour I think reblessing is a fine way to procede. (I think in a way you could compare it to a "seed" object turning into a "Tree" object.)

Now there are times and places for everything. I wouldn't encourage a lot of reblessing, but I dont think it should be just automatically rejected. There are times where it makes perfect sense.