I've used Opera on Windows Mobile before and thought it was OK.
The iphone has a few obvious shortcomings - no java, flash and the ubiquitous copy paste issue.
That said, I got my first palm pilot about 10 years ago, my first smartphone when samsung released their first Palm OS based phone that had a color screen a few years after that, have had a million blackberries and windows mobile phones, treos etc for various jobs and also to satisfy my own gadget lust.
In a big picture sense, none of them hold a candle to the experience I've had with the iphone. I could pick out a few things about some of them that trump the iphone in one way or another. But overall, IMHO, the Iphone just crushes all of them. And that's before you even consider that it's got a built in Ipod or the App Store which just gets better and better all the time.
And that's all I've got to say about that.