Comment 1 for bug 510415

I was able to boot into the old kernel that the upgrade left and edit my fstab.

Here was my entry in /etc/fstab that caused Lucid to hang on boot.
/dev/sdc1 /media/usb vfat defaults 0 0

Adding a 'nobootwait' option fixes the problem.
/dev/sdc1 /media/usb vfat defaults,nobootwait 0 0

As the OP says there was no hint as to what the problem was. Luckily I know my way around Ubuntu fairly well and was able to get enough info to lead me here. I am afraid there will be many that might not be able to so easily find this bug report. So i agree with providing users with a little more accessible information on this problem.