I've also experienced locking problems in 12.04 that were very easy to recreate with a proprietary OpenGL-based program. We reverted back to 11.10 for now.
Different levels of regression. I have several Ubuntu using friends - completely normal users - who constantly need help because the Ubuntu upgrade broke.
I did a 10.04 to 12.04 upgrade on a server the other day. It also broke. Completely standard with no software installed except for Apache. No modifications done whatsoever. Upon booting into 12.04, the screen just flickers. I looked at the log (from ssh) and it had to do with vesafb or something like that. I didn't bother investigating, and did a plain 12.04 install from ISO.
