If you consider how tightly packed the components are in a mobile device reducing operating heat is an important and relavant factor. My n900 is "standard issue" (no firmware updates or overclocking) and it does get pretty warm when I play one of the many console emulators on it. Maybe the 600mhz speed was selected because it offered the appropriate speed vs heat? It's a shame his n900 is so messed up but he must have known the risks before he started. The only thing he can do now is to reflash with older, stable firmware but not use the phone functionality (can't downgrade it). Hopefully the 1.2 update will be soon. If you need a mobile phone you will just have to use an old one during the meantime. This proves the risks are not theoretical but very real. Your n900 probably thinks this: