At the risk of repeating myself, I'll be speaking at the MacTech Conference next week in L.A. I'm actually doing two different presentations. One is on iCloud Document Syncing, the other on Metaprogramming in iOS. In my head, I'm king of thinking them as the "useful" talk and the "fun" talk.
As part of my prep, I've been putting together some examples. Here is another library of useful methods for Objective-C metaprogramming. Specifically, I have methods to simplify method- and class-swizzling. Also, unlike traditional Objective-C metaprogramming--I'm using the block-based API for dynamically adding methods to classes.
I've tried to address all the obvious gotchas (class clusters, KVO, nested dymanic subclasses, etc.), but--obviously--mucking around with classes at runtime will always be a bit dangerous. There are probably a few edge cases that I haven't though of. Take a look at the included documentation and the unit tests, if you have any questions. Most importantly, if you use the code in your own projects (not just when doing exploration coding or debugging), be sure to use it judiciously and test it ferociously.