Every time my phone is rebooted, quite a few HTC Sense battery draining widgets start up in the background as services that poll for information and would kill my battery in just a few hours. Even worse, they somehow get rolled into "Android System" when you're looking at your battery usage. Anyway, kill any services that are running and not using (Mobile IM, Skype, City ID, Music Downloader, etc.), and you'll see a huge difference is battery life the next day. I have anyway.