This is dead simple; Gnome 3 tries to impose Suspend on users as the only true way(tm) to de-power their system; hiding PowerOff behind a modifier key. If suspend fails on your Fedora 16 Machine this is a constant source of irritation.
In short, to avoid a minor rant, suspend is quite a problem area for Linux and is broken on many common chipsets and systems. I have 2 Desktop machines and a NetBook all running Fedora 16, and suspend is broken on all of them, I suspect many others have a similar level of breakage.
Fortunately; the system policy framework on Linux is good; allowing us to simply tell the OS that Suspend is not available. 
UPDATED: The original solution given here worked but was substandard because it was not permanent. Updates to the polkit system would re-write the file we were modifying, leading to an ‘aaargh! dammit.’ moment.
Fortunately folks older and more into the inner workings of this stuff than me have a better, permanent, solution; so head on over to Anttix’s blog for a correct solution.
Do not do the following, see above!
Edit the xml file:
/usr/share/polkit-1/actions/org.freedesktop.upower.policy
.. with your favorite text editor.
Find the XML definition section for suspend:
<action id=”org.freedesktop.upower.suspend”>
…
<defaults>
<allow_inactive>no</allow_inactive>
<allow_active>yes</allow_active>
</defaults>
</action>
Ignore all the Description and Message fields; the bit we are interested in is the ‘allow_active‘ definition; change the ‘yes‘ to ‘no‘.
<allow_active>no</allow_active>
Save the file (you did edit it as root.. yes? 
) and reboot.
Once you have done that Gnome 3 does the correct thing and replaces the Suspend default menu entry with PowerOff. And one of life’s little irritations is now solved; If you have a laptop you might also want to use the Advanced Configuration editor (Part of the ‘gnome-tweak-tool‘ package) to modify behaviour when the lid is closed.
It works, good job
thanks this helped
Unfortunately the files under /usr/share/polkit-1 will be overwritten by next upower package update.
A correct solution is to create a new config file under /etc/polkit-1/localauthority.
/etc/polkit-1/localauthority/50-local.d/50-disable-suspend.pkla
[Disable Suspend]
Identity=unix-user:*
Action=org.freedesktop.upower.hibernate;org.freedesktop.upower.suspend
ResultAny=no
ResultInactive=no
ResultActive=no
Excellent! thank you very much, I’d wondered if there was an even more arcane solution available; and I was right.
I’ll update the main post asap.