Holy crap that was messed up. I recently installed the alpha, then the beta, and now the release candidate of Ubuntu 10.10 Marvelous Merkin on my Sony Vaio M111AX. Problem is, where my laptop could sleep, hibernate, restart and shutdown just fine under 10.04 Lucid, it was now just wedging with X mostly shut down but the desktop background still there ... taunting me.
It turns out the problem is in one of the the Ralink drivers. And since this machine uses an Atheros for WIFI, I really don't need Ralink.
So I edited /etc/modprobe.d/blacklist.conf to add a few lines at the bottom:
It's likely overkill, as the rt2800pci is the particular one that causes the problem on this particular model of Sony. But I'll bet other laptops with similar problems will benefit from this more inclusive list. (And `lsmod | grep rt` will tell you if you have others, in case this set doesn't do it.)
After you edit the file, tell your system to reboot. On this last reboot just after editing the file, you'll wedge like usual, but the subsequent ones will blacklist the ra2800 drivers correctly, and reboots will work just fine. Phew!
Update 20110906: Newer Ubuntu distributions starting with 11.10 (Obsequious Ostrich) include version 3.0 of the linux kernel. Applying these instructions to a 3.0-based system will result in no wifi connectivity at all. If you followed these instructions for a 2.6-based system that you intend to upgrade, you'll need to undo them when upgrading to a 3.0-based system.