according to apple, it's best to "keep the electrons moving' within it, and ideal use would be using it on the bus for an hour or so, then charging it, then using it at home unplugged for a couple hours, then charging it, etc. Definitely calibrate your battery every 1-2 months though. I hear it really does make a huge difference in the life of your battery.
The "keep the electrons moving" was the most retarded marketing ploy I've heard until I saw the Microsoft laptop hunters commercials.
Electrons don't care if they're moving or if they remain attached to the Lithium atoms inside the battery. All batteries degrade, and they degrade at an accelerating rate the more you use your battery.