I got a pesky 1.4 board here that keeps locking up after 10-20 minutes. I thought it might have been ESD-ed RAM but I replaced each chip testing between each one. This didn't fix my problem. Temps seemed to be normal as well. When it locks up, CPU is around 50C and GPU around 40C.
One thing I find interesting is that after I reboot it immediately after the lockup, the flubber animation will lockup but the sound keeps playing until the end with nothing happening afterwards. I don't know if this could be a video encoder issue (since I don't have a spare Focus chip to test) or the sound might just continue playing because it's being read directly from RAM during the bootup/POST process.