To Power Off you use the ALT when you hover over Suspend and it changes to
Power Off. I think this may be changed shortly. I am still on GNOME 3.1.x
but GNOME 3.2 is out and I think that it has a proper Power off option
without Alt. If not, now you know. I don't know who dreams this stuff
up sometimes and how they get into important decision making positions. This
has led many users to say the same thing.

This is a good guide to GNOME 3: http://live.gnome.org/GnomeShell/CheatSheet