I've been unlucky. My first N900 (now with USB port broken) showed a very few random reboots in "ideal" settings, and went OK up to 1.15GHz (it was only hot). Anyway, I only used faster than "ideal" speed settings when playing some large RMVB files (no hardware acceleration decoding, so they need cpu power). Normal conditions in "ideal" settings (hard working with GPS/music/browsing) did never show reboots; apparently the random reboots happened only while accessing the 30Gb data partition. I bought my second N900 a few days ago. I overclocked it with "ideal" (850MHz) settings, soon experiencing random reboots, mostly when accessing that 30Gb storage while playing music (it often reboots in the middle of a specific MP3 song which plays without problems when at 600MHz). Also, it appears to show more heat than its predecessor... Thus, IMHO I guess that slowing a bit the eMMC access (by reengineering its driver) could consistently reduce "random reboots" when overclocking.