I'm sorta approaching this same question from a bit of a different direction: I've never been able to justify an iPhone but have had two iPod Touches (my wife has another one) and will hopefully be getting an iPad for my birthday. If the new iPhone ends up close to what's been stolen, oops sorry, leaked then it may just be enough to retire my iPod.
I've looked at Android and webOS over the last couple of months and have come to the conclusion that every OS out there has problems, some worse than others. In my case it's worked out roughly like this:
iPhone - mostly issues with Apple being a bit too slow with OS updates and control over the App store being a bit TOO tight. On the other hand it's the only one of the three that I'd consider a full, properly-supported platform right now and there are benefits to that control as well.
Android - love the concept, love the support Google's giving it, love the relative variety in handset designs (how varied can a touch phone be after all?), love the cost, HATE the platform fragmentation and slow software updates for anything that's not a base Android phone. Sorry, but when you invest in a handset and apps for 18 - 24 months and build a workflow around that (even if it's just managing and maintaining contacts and media) you need to know it's going to be supported for the life of that contract and Android is utterly terrible at this right now.
webOS - have tried a Pre on a few occasions now and haven't really got on with it. It's a lovely platform but my lord does it feel half-baked and the iTunes sync debacle seriously put me off. Hopefully once HP takes over we'll see some major improvements here but they still need to get developers on board.
Out of the rest... symbian is crap (sorry but it's only really any good as a featurephone OS these days) and WP7 I just like the look of less and less the more I see it. It looked kinda fresh and a little bit funky when it was first announced but now I'm already bored with it.
Here's the thing about Apple and the iPhone OS - they're supporting it properly. I can get an iPhone tomorrow (or, more likely, in mid June when the new one comes out) and my current workflow transfers straight over. All my apps will work (or at least they should do if devs wrote 'em properly) and I already know the basics of how to get the most out of the OS. It'll be supported up to the end of the contract and there's now a well established and mature app market on the device. That means far more to me than getting the latest whizzy hardware (which frankly I won't notice 99.9% of the time) or having the last word in flexibility in my mobile computer (I've long since gotten fed up of tweaking my computing experience).