Several times today, my Mac (10.6 Snow Leopard) has frozen up. The cursor has become fixed (movable, but the cursor does not change), the screen unresponsive (nothing highlights when I roll over it, I can't interact with any program, or the menu bar). This problem has occurred while working in a number of different applications, Chrome, Thunderbird, Xcode.
alt-cmd + esc to open the force quite dialog, which does work. I've discovered that the system recovers, regardless of which application I close, e.g. I get a freeze when working in Chrome. I bring up Force Close and close Activity Monitor, which has been running in the background for a while. Everything now works again.
My current solution is to keep something non-essential, like Activity Monitor running all the time, so that when the problem does occur I'm not forced to FC something critical (and yes, it still occurs when Activity Monitor is not running). I'm stumped as to what this could be, I only have a few (4-5) applications running at once, the load on the system is minimal. The seems to occur when typing, but as I'm using the keyboard 99% of the time (in Xcode or the terminal) that's not really that helpful.
How can I prevent this annoying lock-up?