I have a netbook running Ubuntu Netbook Remix (UNR) 9.04. I switched it to the regular Ubuntu desktop just to try. Before I switched back, I rebooted (the battery ran all the way down). Apparently, this is known to be a bad thing. When you restart, all you get is a blank desktop -- no panels at the top and bottom to allow you to get at any commands.

The fix is described in Launchpad here, but I'm going to summarize it because it's a little spread out in the comments to the bug.
  1. Right click on the desktop and select "Create Folder..."
  2. Double click on the folder you just created
  3. Navigate to "/usr/bin/desktop-switcher" and run it
  4. Switch back to the UNR desktop
  5. Now navigate to your home directory
  6. Show hidden files (View-> Show Hidden Files, or Ctrl-h)
  7. Delete the .gconf, .gconfd, and .config folders
  8. Log out and log back in
This should fix the problem. Now, with respect to the classical desktop, don't do that :-)