The other issue that can degrade batteries is overcharging, but again, batteries these days (and really the devices that these batteries are in) have circuitry in them to ?shut off? the charger when they detect that the battery is full. In short, don?t worry about leaving the thing on the charger.
On a related note, how stable is the Xoom when it is in the upright charger? Stable enough to use while mounted? Stable enough take an errant light impact of the nerf variety without falling over? Etc. etc.
-Suntan