Calibrations - in the most simple terms - are adjustments to the picture settings that give the optimal picture performance. While usually not the brightest settings, the color representation is closely matched so that a true picture can be delivered.
A professional calibration does this with some pretty fancy equipment, and a few hours of adjusting settings. If you're looking for true picture and color representation, then it's worth the money. If you're able to change your settings so that they're appealing to you, you may be best served passing on the service and relying on your own preferences.
C|Net has offered a HDTV Picture Settings forum, and the editors who reviewed our televisions last year offered up some great settings. The one for your particular unit is here:
What is calibration? How do you do it? How often it should be done? I bought a store demo and they suggested calibration but it cost, they say it should give you a better picture.......