I have had the upgrade Brick 4 of my computers. One computer I was able to hit Tab key before the splash screen and boot to an older Kernel. This got me to the Shell and I was able to startx and finish the install. It appears that the system reboots before the upgrade process completes. On one of my Newer computers which just had 11.04 installed, the TAB key trick didn't work. So I held down the esc key to see where it was hanging (Battery) at that point you can CTRL-ALT F2 to another shell terminal and try and recover.
Oddly enough, I have not had 11.10 upgrade work on any of my computers yet.