I am coming from an iPhone and for the most part love the new slick user interface. I did a post about my experience on here at this post:
http://forums.windowscentral.com/windows-phone-7-os-discussion/179841.htm
However the deal-breaker for me that might get me to get another iPhone 5 is the lack of a solid Map App. I understand it's up to Google Maps to put out an application which will most likely never happen. However if Microsoft is seriously taking a run for the Search/Advertising market it desperately needs to ramp up its Bing Maps. Bing Maps is pretty atrocious as it stands now.
Just doing basic searches for gas station will a yield results miles away from your location when there is clearly one less than a mile away. I understand that ads are their business model, however don't completely remove results from searches especially when oriented in a small map location.
This become clear when I was low on gas and was in the Pasadena/Altadena area which is not a rural area in Los Angeles. I manage to get a result from Bing Maps however on my way to the gas station result I manage to find a gas station right off the freeway. The result was still pointing me further down another mile. I even tried searching for "gas station" while fueling, and still Bing Maps promptly pointed me to another gas station a mile away. This is unacceptable. I tested out the Garmin App which yielded even more gas stations much closer what Bing Maps was given me, including the gas station I was fueling.
Also use Yelp a ton for searching new places since I'm constantly driving around new areas. I also travel about every four months to new cities around the states. Yelp and Google Maps were crucial to me. Yelp was probably more important to me since it provided user reviews, and photos. I could live without the Google Maps if the Yelp app at least was up to par with iPhone and Android offering. Again I understand it's up to Yelp developers to put out a solid application, however this is probably the most important 3rd party app that needs to be supported.
I am taking a trip to NYC(not my first time) around Halloween which I will be out there for about a week. The fact that Bing Maps has performed so poorly just around Los Angeles has me nervous enough to consider going back to iPhone. Also the lack of MTA directions on Bing Maps might be just enough for me to switch back. Seriously Bing Maps is probably Windows Phone 7 biggest issue in my opinion, even more so than multitasking, and all the other features coming with Mango.