For any KDE users out there using FC2, you may have noticed that KDE menu editing is broken out of the box. You can change existing items, but you can't add or delete items. I have found that if you copy the contents of /etc/xdg/menus to ~/.config/menus, you can then add or delete menu items. You still need to be a bit careful as it doesn't seem to handle moving items from one category to another very well.
It would be nice to have menu editing enabled in GNOME as well, but that doesn't seem like it's coming anytime soon. I know that menu editing isn't important if all that you use are RPMs created for Fedora, but not all software comes this way. I usually like to grab the latest Firefox as it comes out and a menu item needs to be manually created for it as it is shipped via a tarball.
I have found that if I go to ~/.config/menus and remove all files except applications-kmenuedit.menu that I can edit the kmenu with the KDE menu editor without any problem. I *think* the other files are put there by gnome and since I don't generally use gnome I don't need them. I'm not sure how one might work around the problem if they wish to use both gnome and KDE.