Offer clear instructions, and possibly a "recovery" type menu, when X doesn't start

If, for whatever reason, the system comes up in text mode, there should be more information than just "Ubuntu X.XX login:".
Proposal: Display a (centered) header text like "Press Alt-F7 to go back to graphics mode, or type your login name and password to login in maintenance mode."

If the user logs in, there should be a possiblilty of starting common maintenance tasks that might be a reason for X11 not starting up: the graphics card or display might have changed, the file system (especially /tmp and $HOME) might be full, there might be errors on the harddisk, etc. A curses based menu would probably be sufficient.