My biggest problem with Gnome 3 (and the number one reason I abandoned it in favor of Xmonad, which I've come to like quite a lot), was that it breaks the UI concept of the modifier key.

Simply pressing and releasing the super key (with no other keypress in between) triggers a change of state (bringing up the "overview" or whatever it's called). The modifier key is such a basic interface concept that I struggle to imagine why they would go out of their way to break it -- any way I look at it, it's just monumentally idiotic. And best of all, I could find no way of disabling it.

Admittedly, they're not the first to do this. OpenOffice has done something similar for quite a while (pressing and releasing a modifier key brings up a menu); that was one of the many things about OO that pissed me off. Nevertheless, precedent is insufficient justification for such a thoroughly moronic change.

I've been wanting to rant about that for a while now, glad to get it off my chest. Thankfully, Xmonad is fantastic, so in a way I'm grateful to Gnome 3 for leading me to switch to it.