I use mine evenly.... a perfect mix of business and personal use.
For business use, I use the calendar, appointments, alarm, calculator, GPS / maps, web browsing, and email.
For personal use, I use the calendar, appointments, alarm, GPS, web browsing, email, weather, youtube, CNN / MSNBC, Myspace, yellow pages, loopt, My to do's (to do list), notes, calculator, contacts list, camera / photos, SMS text messaging friends, ebay, paypal, sports tap (for nfl), google talk and aim, aol radio, shazam (for when i cant remember a song name), box office (for checking movie times), check please (when my friends and i go out to dinner), shopper (duh!), flashlight (jinglin them keys in the middle of the night), and my Looooooong list of games when i'm stuck "WAITING" anywhere. Oh, and lockbox, for my secret stuff.
To sum it up, I use the iphone for just about everything you can think of. I also listen to music on it when i'm working out, and watch a movie on it during my lunch break.