There are so many conflicting pieces of advice out there with regards to how to look after the battery on your portable device. Some say that you have to frequently let the charge run dry, then charge it back up to maximum on a regular basis. Others say that as there are sonly a certain amount of power cycles in the battery, leaving it connected to the mains permanently will improve the life of the battery.
These are the facts, however, as I see them and this is the maintenance I use to ensure my MacBook Pro battery lasts as long as possible.
The way I work is to ensure that the electrons in the battery are always moving. Keep those guys moving and your battery will reward you with a long life. This means that as soon as my charge hits 100%, I unplug.
Apple recommend that a battery will run for 300 cycles before the maximum of capacity of the battery hits 80% of the original maximum life. My MacBook Pro is quite new and I have only run 63 cycles currently. However my battery still has 100% of it's original life left, so right now I'm not going to argue with that. I have a friend who runs the same battery diagnostic software as myself (Fruit Juice - fantastic value for £6.99 - you have to check it out) and he is sitting at 715 cycles with 94% of the original battery left. As said, he follows the same charging routine as I do.
If you use Fruit Juice, it will recommend when you should charge/unplug your battery for optimum life and I use the heck out of this software. £6.99 is nothing compared to the cost of replacing parts/devices and it also gets you into good habits with all of your other devices as well as your friends/families.
So ensure that your battery is always active, whether it's active through the action of charging up, or active in the action of discharging and providing power to the device in order to maximise battery life.