Wouldn't it be so cool if the iPhone had another field in the "Usage" screen that shows how much time you have left on the battery (not percentage)? Think of Apple's MacBooks. If you look in the battery menu it will show you how much time is remaining (an estimate).... based on what you've been doing (example: watching a movie). I think the iPhone could be smart enough to be able to do this. That way people will know for sure why their battery doesn't last as long as they thing it's going to. Lets say, you're using GPS one day and you look at your usage and it says "about 2 hours remaining" ... you might say... wow, I better take it easy if I want this to last me until the end of the day... so then you start listening to the iPod for a while and now it says "about 18 hours remaining" because if you KEEP listening to the iPod only, that's how long it will last. Based on your activity history.