I was having a wait and see approach to WP7, and when it initially came out I spent a bunch of time playing with the SDK. It’s a nice SDK and I think that there is a lot to like about WP7, but I think that they where very smart in breaking backwards comparability and making a clean break from windows mobile thus removing one of the old Microsoft albatross, the fact that they are going to use some IE7-8 mobile Frankenbrowser is going to kill the phone. We basically have one standard browser across all the major mobile platforms, as Webkit is used on iPhone, Android, WebOS, the latest Blackberries, and Symbian - WP7 is going to be the odd man out. And while a lot of sites sniff for iPhone now, I can quickly see sniffing for webkit to be the new standard.
No web designer is going to waste time designing two mobile websites so either mobile goes to lowest common denominator websites or they are designed for webkit and WP7 either looks bad or gets to render the desktop version.
As I spend more and more time browsing the web on my mobile device, I look for sites that have mobile versions of their website. And I know that I am probably not alone in thinking about the mobile browsing experience when I buy my next phone. If a bunch of ex-iPhone users move to WP7 and their browsing experience gets worse, you know that they will be unhappy customers. I know the mantra now is that it is all about the apps, but I really think, whether people know it or not, it is all going to be about the browser.