I have Ubuntu 11.04 and I works perfect.
I do not know what happened but for no reason the logout, restart and shutdown options disappeared from power menu.
I did restart it more than one time maybe it will solve the problem. also, I did all the updates and still the same thing.
I check the gconf-editor on /apps/indicator-session, all the options of suppress_* is not checked.
I've also tried purging the session indicator packages before reinstalling them:
sudo apt-get purge indicator-session indicator-applet-session sudo apt-get install indicator-session indicator-applet-session ubuntu-desktop
I do not know when this problem happened but 2 weeks ago was every thing fine.