In beta 5, about one in five times that I close my MacBook Pro display and set my machine to sleep, I get an instant reboot of my MBP. Obvioiusly this kills everything running. One time, though, it looked like my MBP went to sleep, but actually didn't. It ran all night, very hot, and when I got up to wake up my machine, I noticed it was running with the screen closed. I opened the screen, but the machine wouldn't come back to life. The only way to reset it was to hold the power button.
