I've installed Natty on an older Samsung desktop at work. It's a shared machine that needs no screen-locking, passwords, or anything else. (Perhaps it should have those features, but nobody would use it then.)
Anyway, after the screensaver is activated, and subsequently deactivated, the interface often (though not always) freezes. By "freeze," I mean that while the mouse pointer moves on the screen, the system (Unity, perhaps?) doesn't respond to clicks or normal keyboard input (Ctrl+Alt+F1 does work, however). Additionally, the clock in the panel stops updating and continues to display the time at which the freeze occurred (which appears to be during the time the screensaver was active). The only way I've found to recover is to issue
sudo service gdm restart.
After discovering this problem, I disabled the screensaver. That seemed to cure the problem for a while, but now it's back, showing up after the monitor has gone to sleep. I thought someone had fiddled with the settings, but it's unlikely anyone would do so, and I couldn't find anything amiss.
Any idea what's causing this problem and how to fix it?