My wife has a MB, now 50 months old, which she has
never unplugged from the wall outlet. It has been used on battery during that time only when I borrowed it.
The last time I checked it about a month ago, the original battery had less than 30 cycles, it has been calibrated exactly two times - only because I had borrowed and used it until it died - and the current capacity is currently 5% higher than original.
Meanwhile, my 56 month old MBP, used 65-70% plugged in and 30-35% unplugged with monthly calibrations as recommended by Apple is now on it's 3rd battery with replacement after the battery hit 1-1.5 hours max uptime.
Read Apple's recommendations at:
http://www.apple.com/batteries/ - Follow all the links and educate yourself.
After you've done that, it's
your computer. Disregard what everyone else says about the battery in
your computer, iPod, iPad, iPhone, Blackberry, HTC, Android device, car, boat, TV remote, mouse, shall I go on??? Use the thing the way
you need to use it. Forget about the freaking battery the same as you do with every other device you use that has a battery, keeping in mind what you've gleaned from Apple's recommendations and replace the battery when it needs it.