Extending that, an outliner can be a great way to deal with this stuff. The problem becomes the self-referential nature of OO systems. Outliners are good when you get to the method of interest, but then you have the problem of browsing senders and implementers.

Still, there's nothing worse than a Smalltalk without a class category list. Smalltalk/MT, for example, just had a class hierarchy browser, and the category class member variable was left blank. I found it very hard to know where to start looking for behavior.