Somehow I would have to agree with you. When I first got the iPhone I had a couple days off from work and after using the phone all day by the time it was 6pm the battery would be quite low around 20-30%. Over the past week or so, it seems like that has improved, I use the phone all day (mail, sms, safari, dozens of long phone calls, beejive, the wifi is on for a couple hours) and still even now its 6pm and my battery is over 50%.
Maybe iPhones had a secret firmware update