Gnome has just upgraded their version and there is a bug which breaks the menu. This affects anyone who is migrating from any previous versions of gnome to 2.26. I am not sure about Linux Distributions which use binary packaging systems but on Gentoo Linux There are some things that break on the upgrade.
Once I got all the packages compiled and installed, I started up my new desktop and to my dismay the application section of the menu no longer worked.
So there are actually two fix’s for this depending on the way you have gnome set up.
If you are using a login manager and lose your menu, please re-select gnome as your session at the login prompt. I do not use a log in manager so this didn’t work for me.
If you start gnome by hand with the command startx then you need to set a enviorment variable in order to get your gnome-menus back.
Now its up to you where you put this of course, I guess you *could* put it in your .bashrc file however I normally put stuff like this in a rc.local file. Since I am on gentoo there is no rc.local file but there is a similar file. I just added the line to it and rebooted and my menu issues were fixed.
infidel ~ # cat /etc/conf.d/local.start
# This is a good place to load any misc programs
# on startup (use &>/dev/null to hide output)