Someone above suggested discharging a battery to empty helps with the charge capacity. I say it depends on the type of battery. In my Treo 700, I have a LiOn battery, the original battery for over 6 years now. I plug the phone in whenever I can (while sleeping, driving, sitting around the house, etc.). Over the years, I have rarely let the the charge go below 60%. This battery still holds a charge as good as new.

I have heard that LiOn batteries don't have a memory. In other words, it doesn't matter if you take the battery down to zero. Anyway, because of my experience with how I have treated this LiOn battery, I'll be treating other LiOn batteries the same in the future. Nevertheless, on my next phone, I will probably be thinking, "They sure don't make 'em how they used to."