If you are getting at least one day from a full charge, then that is great for the current generation smartphones. They require more power than the older ones, and therefore the battery may not last as long. It is OK to keep it on the charger and topped when in the office or at home.
As for the drain could be a lot of things. Apps running in the background, data intensive apps, BES, WiFI, etc. Plus if you are in a cell 3G fringe zone the device would be constantly searching for a signal. Programs Running in the Background Maximum Battery Life - BlackBerryFAQ