When you wrote that, did you know that if the sticky-keys setting is set and you accidentally hit a modifier key, then you can undo that by hitting the key 2 more times?
(I've been using OS X's sticky-keys setting with Emacs for years, BTW.)
Yes, I recall having noticed that, but still didn't feel very natural, probably because I use different systems (not all of them OS X even) and this complicates habit making.
(I've been using OS X's sticky-keys setting with Emacs for years, BTW.)