I just upgraded to natty and after a few reboots i get the following message midway during boot:
start: Job is already running: mysql

A quick google search unearthed year old bug reports, but I am unsure if those are the issue here.

Just before it broke I installed a proprietary ati driver from their website, and tinkered with compiz control.

I can enter any tty just fine, but I don't know how to get mysql to run properly and resume booting