the newer laptops use lithium ion batteries which are pretty resilient so no probs leaving it plugged in. You will want to drain the battery from time to time, but that's about it.
One thing to remember that when you're on the battery the system will try to cut down it's power consumption so its slower, the display will be dimmer, hard drive will spin down when idle for a few minutes, then have to spin back up again when it needs it, so the system has to wait that extra second or two to access the Hard drive...another delay.