I mostly like gnome-shell, and much prefer it to Unity at this point. (In reality, both are greatly lacking in polish.) However, when using fullscreen applications, I notice that the hot corners do not go away.
This is most notable in VirtualBox which I need to run to access windows programs for my job. The gnome-shell notification area covers up the bottom pixel of the entire UI, making the windows taskbar largely useless-- you go to click anything, then need to mouse up a tiny amount for windows to actually see the click. This behavior is particularly annoying. The [Windows] key also fails to be passed to the applications that listen to it, as gnome-shell captures it instead.
I sort of wish I could use gnome-shell with unity's notifications instead, as that's my only real gripe with it. Otherwise, maybe it's a virtualbox issue. Is there a way to get virtualbox to play nice with the new shells? (This might affect Unity as well, I haven't tried it.)