All the newer laptops (past 3-4 years or so) utilize Lithium Ion (Lithum Polymer for the MacBook) batteries which aren't affected by the memorization issue the older Nickel Cadmium / Nickel Metal Hydride style batteries suffered from.
Lithium Ion based batteries do loose a small amount of capacity each time you cycle (a full discharge and recharge) the battery, which is the nature of the beast.
You'll actually cause more loss by unplugging it, since it'll draw some current when turned off to keep settings current (which, over time will slowly add to the number of cycles used). So just leave it plugged in and follow Apple's directions on
conditioning and maintenance of your battery.