It was necessary with the old "dumb" batteries and the nimh/nicads. Modern lithium batteries do smart charging, which eliminates the need for calibration.
BatteryBar constantly monitors the status of your battery as you use your laptop. As it monitors your battery, it keeps historical data on your battery and provide you with a very accurate estimate of how much time is remaining on your battery.
I just use this http://osirisdevelopment.com/BatteryBar/
It does a good job on all the laptops so far.