I own a Dell 700m for taking notes on and wireless internet in class... I bought the more expensive battery which lasts about 5.5 hours. Ive never run out of power in class.... and I can leave it on pretty much all the time and not worry about it. Then again I have my PC in my dorm, so if this is your only computer I might recommend something more powerful.
Here is a picture:
http://pc.watch.impress.co.jp/docs/2004/0823/dell.jpg