What bb are you coming from? I saw that the 9700 and iPhone 4 have the same battery life on 3G. The bb has better battery life on edge. But I get 10 hours of use on 2g on the iPhone 4. So it's not bad at all. I get 6 hours of usage on 3G. My bb got around the same. Maybe 7. But don't forget that the iPhone has a larger screen and a more powerful processor and more pixels to control. And more ram to manage.
I was a bb user for 5 straight years. Look at my sig

hehe I'm on the iPhone until a killer bb comes out.