I've had an iPhone 3G. I don't think I'll be getting the iPhone 4 as I'm content with my HTC and Android (give me Froyo or I'll delete this post!).
I'm still very much watching the market though. Perhaps the iPhone 4G will be more impressive. Perhaps it'll have three cameras.
Did you know there are designers who wanted the iPhone 4 to have 3 cameras? This video explains all