Very helpful article from Farhad Manjoo about preserving battery life in modern electronic devices.  It starts out somewhat depressing though:

Buchman also runs Battery University, a very helpful Web site for battery enthusiasts and engineers. I asked Buchmann how we can make sure that our batteries last a long time. "There is not too much to discuss," he began, and then launched into a conversation exploring the numerous frailties of batteries. The upshot is this happy factoid: No matter what you do, your battery will become a useless piece of junk—one day it will reach a point where it can no longer be charged, and then you'll have to recycle it. It will die if you use it often. It will die if you hardly ever use it. It will die if you charge it too much. It will die if you charge it too little. You can pull the battery out of your camera, stuff it under your mattress, and come back for it in five years. Guess what? Your battery will be dead. And when I say dead, I mean dead—not that it's run out of juice, but that it can no longer hold a charge.

That said, the great sin of battery life is over-charging.  Don't do it.  I've been guilty and I'm going to stop.

Ideally, Buchmann says, you should try to keep your battery charged from 20 percent to 80 percent. Keep in mind that these are guidelines for ideal use—it's generally inconvenient to unplug your machine before it goes all the way to 100. But even if you're not on constant guard, be mindful of charging your machine constantly, well past when you know it's full. You also should be conscious of letting your battery run all the way to zero.

Try to keep your laptop as cool as possible. The best technique here is to charge up your battery when the computer is turned off.

Pretty handy.  The basic rule seems to be the 20-80 and keep things from getting hot.  Words to live by in our gadget-filled age.