Will leaving your notebook constantly plugged-in kill your battery faster? Gina Trapani is exploring the issue after a friend's battery wouldn't charge after only two years. Though HP and Dell support pages weren't quite definitive, Apple clearly cautions against it:
On a page dedicated to maximizing your MacBook's battery life and lifespan, Apple says:
Apple does not recommend leaving your portable plugged in all the time. Apple recommends charging and discharging its battery at least once per month. Need a reminder? Add an event to your desktop's iCal.
Apple also says that you should store the battery with a 50% charge if you're not going to use your laptop for more than six months (otherwise it could fall into a deep discharge state, and not be capable of holding a charge).
Many laptops—PC and Mac—use Lithium-Ion batteries (as opposed to Nickel-metal hydride), so it's a good reminder to make sure you read your freakin' manual. What's been your experience with laptop batteries? [Smarterware]