Keyboard & Trackpad unresponsive? Reasons?

So, not as general as the topic may suggest...

I was just chatting with a friend on iChat and my keyboard and trackpad became completely unresponsive. I had sent a message to him, then went to reply to his response and there was just nothing there as far as input was concerned, both were completely unresponsive.

The only other running apps at the time were Mail.app and FontExplorer X Pro (which is always open for me, much like finder)

Anyone have any notions why something like this would happen. In 6 years of Mac portable use (powerbooks and Macbook Pros), I've never had this happen to me.

I had to hold the power button for 5 seconds to shut the comptuer down.