I used the iPhone OS for ages, and I think it's a brilliant OS, but there are some restrictions that annoyed me to the point where I sold it. I can't live without multitasking or flash. Other missing features at the time were also MMS, forwarding/deleting messages and a few others.
The only real advantage the current iPhone has over other phones for me is the massive selection of apps. I know that Android has a lot of apps too, but they're not as high a quality as those for the iPhone app store.