It can also make the computer uncomfortably hot to touch. Battery life varies wildly from one model to the next, from 80 minutes to 5 hours. Make sure you get a lithium-ion battery, it is superior to any other rechargeable battery currently on the market. Not all of them will let you use the floppy and CD drives at the same time. Most have the power brick on the AC cord, which can be a bit inconvenient.
Keyboards are smaller than on a desktop.
Play with lots of them before you choose. I recommend you buy an extended warranty. The major vendors offer a measly one-year parts and labor. Laptop parts are waaaaay expensive, so the extended warranty will pay for itself the first time you have trouble. They are most vulnerable, being out in the world getting knocked about.