This probably isn't most people's problem, but I've certainly seen something crop up that looked like "system logged me out at random", and solved it:
The VSA will let a single account log in multiple places. If one of them logs out, the rest also get logged out at that time - it's a security feature!
What can happen, I think, is this; if I am logged in on machine A, then log in on machine B, use it for a while, then close the browser (without clicking logoff in my VSA), somewhere a counter is started that as soon as my session from machine B *would have* idle-timed-out, my session on machine A looks like I got "logged out by the system for no reason". But the reason seems to be the idle session timer from another session under the same username. Obviously that isn't going to explain every instance I'm reading about in this thread, but hopefully it helps explain something!
