Problem mapping keyboard shortcuts in GNOME3

just ran into the answer actually. It's because the windows key is mapped to show the activities window. You need to disable that in order to get the shortcuts working. What worked for me was to go into region and languages, under Alt/Win key behavior click meta is mapped to left win key.

It seems that Linux immediately translates keys even when they are part of a key combination, so the left win is sent to the gnome bypassing the key combination.

Read this message: http://mail.gnome.org/archives/gnome-shell-list/2011-May/msg00291.html

I got my shortcuts to work doing what is described there (mapping Left Win key to Meta under 'Region and Languages'); I believe that I didn't need that in GNOME 2.