After updating to Ubuntu 13.10 (Saucy) there is a bug causing menus to break. More details of the bug can be found at the Launchpad discussion here.
Thankfully it's not difficult to fix temporarily and solving the problem involves closing down Eclipse and running the following command in a new terminal window:
sudo gedit /usr/share/applications/eclipse.desktop
Then enter your password and a text file will open. Simply replace the file contents with:
Exec=env UBUNTU_MENUPROXY= eclipse
You may need to remove the line
Exec=/opt/eclipse/eclipse if you installed Eclipse from the Ubuntu Software Centre or you may need to modify the file path if you installed Eclipse in a different directory to match your Eclipse executable directory path.
This issue affects a lot of Android Developers who no doubt have wrestled with Eclipse ADT/Ubuntu update related issues before. It's definately cause for Ubuntu users to watch Android Studio ALPHA/BETA version development more closely or go over to Studio now if they haven't already.