That's a very good question actually. What I think is imporant to take out of all this though is that, except for using my phone to record HD video as I did at least 5 times today, I'm using my phone EXACTLY as I have used my 3GS before. Using my 3GS like this in the past has, AT MAXIMUM (read:1 time) gotten me 6 hours of battery life. So, being that we are approximately mirroring the same conditions, it blows my mind that this phone gets 4 hours more with all that it does. Nonetheless, I'll try and answer your question.
Today, in non-sequential order, I've sent maybe 6 PING's (through PINGchat), made received 3 calls (2 short 5 min ones, one long ~40 min one), used the Apple Store app to look up MBP sleeves, checked periodically and responded to a couple emails, previewed many of the videos I've made, used Safari for maybe 15-20 min total between Gizmodo, engadget, macrumors, used Maps to find a store location and then used it to guide us to the store approx 5 min until I thought to use Navigon (which I then used for maybe 5 min, and wow is the i4 GPS lock awesome), used Grocery G to compile a grocery list and left the app open as I perused through the store and checked off various items within it, listened to my iPod ALOT today (alotta of classical music as I studied, JUST like I did on my 3GS), used the camera app EXTENSIVELY to record HD (LED light on) video of various cadaver musculature in our anatomy lab, used the weather channel twice to check local weather, made maybe 15 texts messages total, used the Netter's Anatomy app all through the day for maybe 4 hours to tag body parts, and finally checked out the app store once or twice for some searches.
Hope that answered it.
