So now that we have a few people with this issue, let's try to figure out what may be causing it (other than just Lion being crap).
What special drivers are you guys using? I'm using a Wacom Bamboo graphics tablet driver, but never had issues with it before Lion. There's nothing else really that runs in the background.
My logouts generally happen when I feel like I'm running out of RAM (I have 4 GB), especially in Photoshop, when it's doing something complicated and I switch to another desktop. It has already crashed twice on the desktop-switching animation. Maybe it's related to multiple desktops?
Once it happened while waking the computer. I woke it and boom, logout.
How do the logouts happen? I get a spinning grey wheel on top of my frozen desktop, it looks like this (it's not an actual screen shot but a montage I did to explain what it's like):
View attachment 301279
After that, my entire screen goes grey for a few seconds, and then I'm presented with the login screen where I have to type in my password.
That's all I can say really