my main use (the official reason why I bought it):

Note taking in class. Xournal does the job perfectly. (also, I always (read sometimes) loose my paper notes :[ )

aside this: games keep me occupied during boring classes
mp3 player
video player (if there are any good movies i've heard of...)
last minute essay finishing (when that last minute is on the bus, or while I'm walking somewhere)
calendar (+schedule)
e-book reader (fbreader for this)
VNC viewer when I forget something at home

no GPS (I have the n800)