I have been using kde with openSUSE 11.4 64bit, and I tried to install gnome 3 with 1-click install to check it out.
It seems to be working well, but I thought in Gnome 3 the super key (mod4, windows key) is supposed to open the activities, bit in my case nothing happens.
I tried to set global shortcut in gconf-editor - metacity but have had no luck.
I’m not sure if the cause of your problem is the same as mine. But in my case, in ~/.Xmodmap, for some reason I had the following:
keycode 82 = Super_L
Which was interfering with Gnome’s super key recognition, I guess.
So I commented that line and did $ xmodmap ~/.Xmodmap and now it works fine. Logout-login might be needed.
See if you have any key remap setting and if you have any Super key related item. Hope this is helpful.