ive experianced a couple different actually..

Once = computer stayed on all night, next morning all applications failed to launch (gave me an error), had to reboot.

Everyother time = left PC on all night (without azureus) system log says (?:??am) We crashed at 0x0000....forgot the numbers)

with azureus i think its a Java issue, i dont know, ill leave it on again tonight and get a log