is it bad to leave my MacBook Pro charge while using it?

I was wondering is it bad to leave the charger plug attached to my macbook pro while using it? some of my friends say it is bad for the battery and shortens it's lifespan...is that true?

No, not at all. Just make sure that when you plug it in to charge that you let it completely charge before you unplug it.

Once it's fully charged, the battery stops drawing power from the adapter.

...and make sure that at least once per month you completely discharge it (i.e. cycle the battery). This is advised to maintain battery life.

Its definitely not bad to leave in it while using it but its always nice to let your battery die down and then charge it back up while its off. it maintains the battery life and lengthens it. Just don't leave it plugged in 24/7 or your battery will die really fast.

Kial

Here's what Apple recommends:

http://www.apple.com/batteries/notebooks.html