I've had an iphone since one week after launch almost 2 years ago. It is a great phone that is easy to learn and use. Just pick it up and everything makes sense. The 3g has better sound, reception and also has GPS over the first generation.
I've had a blackberry for almost 2 weeks. First was an 8220 and after about a week I traded it in for an 8900. It's a very nice device and does the basics of what I need very well. However, the iphone does soooo much more. The larger screen and the fact that it is a touch screen is something that really makes a difference. That interaction makes the iphone a much more pleasurable experience. Given the chance I'd go back in a heartbeat.
I'll have to stick with the 8900 for now. I'm glad that it is a very capable device.