all phones heats up but to the point of blowing is i don't know. i guess prototypes were abused like there's no tomorrow to know if it'll be dangerous eventually or not. so i guess just don't try to push your phone very hard if it heats up too much...

anything that is complicated programs like flash / joiku or connected to 2g/3g seems to create heat more...

my htc kaiser heats up too when i abuse it using slingbox. so n900 isn't an isolated case...