Mine has got better with use, too. Give it time, and see if the upgrade to Android 2.1 helps...
You might find it helpful to get Advanced task Manager from the Android Market, too, to ensure that you are not running too many applications in the background. Also, try Menu - Settings - About phone - Battery use to see what has been using the battery. You might find it helpful, for example, to adjust the screen brightness, or to keep the wifi off when you're not using it. Both of those can get very hungry.
