I have an iPhone and absolutely love it. It's pretty simple to use. I'm very happy with the interface and keyboard recognition, and the screen is very crisp. The responsiveness is pretty quick and the design is pretty sexy. Everyone wants to look at it. Makes a great conversation piece with some of the females!
The battery life is not a real issue. There was a lot of hooplah about poor battery life, but I get about 2 days of use with a single charge. That's with checking mail (auto check every hour), a bit of surfing, and talking on the phone... a lot. I usually charge it everyday though. Despite the reports on the web, even though the battery is not user replaceable, it will maintain 80% charge capacity after 300-400 charge cycles. A charge cycle is completely draining it until the battery goes dead and then recharging it. Drain it to 50% remaining and then you recharge it, then that is considered a half charge cycle. So it will take more than a year for most people to wear down the battery to where it only holds 50% capacity.
Some of the downsides: inability to natively install medical apps (ePocrates, Pepid), lack of voice dialing, lack of Flash support in Safari.