I'm an iPhone 3G user for over 18 months now and to date it has served me well. My first introduction to the 'smartphone' market and to be honest it does that very well. I would imagine most people don't need true multitasking, they just deal with it because it isn't a problem.
I am, however, at the point where the little niggles with the os and how it operates are starting to annoy me. I really do like the idea of being able to choose a specific song whilst in the middle of something, and not losing it. I like the whole way Android deals with applications and the data and how any app can access it to share between the apps on the phone. I'm also keen on the idea of being able to customise the ui and home screen which you cannot do with the iPhone unless you jailbreak it.
I think I've now got to the point where I've outgrown the closed nature of the os on the iPhone and almost demand that it does what I want, not want Apple think it should be. I have a feeling that aslong as the phone itself is nice to hold and comfortable, then there is no reason why an HTC desire should not be great for me to use and purchase.