My Toshiba A75 laptop previously had a problem with suspend and switch-user. Before I clean-installed Maverick, the problem was likely due to confusion in configuration due to dist-upgrades.
The system was a lot cleaner and more stable after the Maverick fresh install, but there was one last niggling bug. Most of the time switch-user would work, and often suspend and restore would work, but when they'd fail they'd show "atiixp: codec reset timeout" and other dmesg errors. When switch-user or restore from suspend wouldn't work, they'd show that or another atiixp error and the laptop would then hang. I'd have to turn it off and on (I didn't try the magic sysreq keys since I'd never used them and just plain didn't know how to use them :-).
I finally got around to trying noacpi (edit /etc/defaults/grub and set GRUB_CMDLINE_LINUX=" noacpi ") and from testing tonight it looks like it's very stable. I've restored from suspend several times and switched users a lot more time.
Previously I thought it was failing because I was doing something with video or audio, so I viewed a video, switched to another user and suspended while that other user. Restore worked fine.
Over a week or two of use we'll know if noacpi is a good fix or if it working now is just a fluke :-).