> I had one (very productive) coworker who would slip intentional bugs or style violations into his changes to see if the reviewer was paying attention.

I've heard of this process ("bebugging", the opposite of "debugging") being used for statistical QA analysis. If you purposely inject 10 bugs (don't forget to remove them! :) and QA or fuzzing finds 7 of them plus (say) 42 other bugs, then you can extrapolate that you have about 18 undiscovered bugs (10/7*42-42 = 18). This assumes your 10 injected bugs are representative of the actual bugs you find, which is harder than it sounds.