I've had this issue twice today and is troubling me a bit. As the title already summaries; without notice, the keyboard and trackpad seem to get unresponsive. The system is actually still running (seeing animations and other stuff still happening). The keyboard power button does actually work, pushing it will summon the screen to logout, restart or shutdown, but I can't actually hit any buttons (ofcourse). So I eventually hold down the power button to power down and then power up again, after this, the problem seems to be resolved.
I don't know if this would be a hardware or a software issue. And I'm wondering if someone knows this problem? I've updated my Macbook recently to 10.8.2.