I recently tried booting into the Grub2's menu entry "Ubuntu GNU/Linux, with Linux 3.2.0-24-generic-pae (Recovery Mode) just to see what was there. It booted successfully, but I had no idea what to do after I was there. My question is where can I find some documentation on the recovery mode and what to do if I truly needed to be there. I'm running Ubuntu 12.04.
The recovery mode is normally used when you need an exclusive admin access to your system. You normally go into the root shell and recover/repair the system through the command line.
* If you have Ubuntu Quantal (12.10) or earlier, omit step 4 (the recovery mode menu items are displayed on the top-level menu).
** If you reboot, there is no need to hold the Shift key in step 3. The GNU GRUB menu will continue to be displayed automatically on each boot until a normal startup of Ubuntu completes. To configure GRUB so the menu is always displayed, even after a normal startup, see https://help.ubuntu.com/community/Grub2/Setup.