I've always been told to wait till the batter is close to being dead (maybe 10%) and then charge. I don't go by that but my battery is usually close to dead by the end of the day anyway lol.
I charged my curve whenever I wasn't using it and I did this for over a year with no ill effects on the battery. I cant leave the house without a fully charged battery, just like I cant leave it without my wallet. lol