I use it to replace my laptop. Going to invest in one of those virtual laser keyboards though, as the small keyboard can get cumbersome when typing lecture notes.
Dragging a laptop around to do email/internet/word processing at class or work ended up being cumbersome. It was rather heavy (well alot more than a BlackBerry), and battery life is an issue, along with finding wifi or hooking the BlackBerry up to the laptop.
Using the BlackBerry as a laptop replacement for me is very nice, no more carrying around extra things, no worry about when the battery dies (well unless im going to do more than like 6 hours of work online; doing 3 hours straight gets the battery to around 60% while in a weak signal area [of course brightness is turned down]), and I never have to consider finding wifi or hooking extra things up to go online. - Speaking of online, its nice to leave everything running on the internet when I go from place to place. Laptop have to turn it off, disconnect, when I get there turn it back on.
So yeah, I use it for email/data/phone.