I hope I can add something to this discussion by summarizing a few previous points and highlighting a few new ones:
- Battery longevity is greatest when you store batteries at relatively low voltages and temperatures. However, it must be high enough to account for natural discharge that occurs during storage, so that the voltage doesn't dip low enough to cause a deep discharge, which will also hurt longevity. (from the batteryuniversity article)
- In general, charging to higher voltages and discharging to lower voltages gives you longer battery runtime, but lesser life. Too bad you can't change the charging thresholds so that you can choose your own balance between runtime and longevity. By the way, the power control panel on most Thinkpad laptops will let you choose charging thresholds.
- When a device is continually topped off, it only requires a trickle charge, which generates less heat than the normal charge current. Every time you discharge a battery enough to induce a normal charge current, you're subjecting it to that much greater heat. You'll have to decide whats worse, a little more heat for a longer time, or a lot more heat for a shorter time.
- When a battery meter shows "100%", it is not the maximum capacity of the battery. Assuming a sensible engineer, the charging circuit has been designed to charge the battery to a voltage that is safe to maintain. So keeping your device's battery at 100% isn't necessarily what you would consider 'overcharging'.
Keeping your Touchpad off the dock will possibly improve your battery longevity. If you wanted to be really serious, you could try to maintain that ~50% charge level for longest life. But really the battery software has already been designed to help you get a good balance of convenience, runtime, and longevity, and most people should not worry to much and let it sit there to charge when not being used.