I dropped WP7 out of frustration with MS. I used to develop some of the models for HTC and do some XDA-deving. Over the course of 15 years, I've learned a very important lesson: If it's MS, all support goes out the window and it's a DIY job for every Windows Mobile phone and now WP7. Not only that but I think the WP7 interface is pretty ineffective for mobile use. It's primarily designed for people that want active content on the background and people I like to call "swipers". Look below for my definition. Android reduces on the number of moves it takes to get critical information but when launching apps, the 1-2 seconds adds up over the course of a year. The math for this is as follows: let's assume a 1 second addition to application launching. Let's also assume you open 20 apps per day (that's pretty conservative). That's an additional 20 seconds per day that you're spending opening applications. 365 days per year means that it's 7300 seconds which is essentially 2 hours per year you're wasting on extra movements inside the OS. That's a full length movie right there or an additional 2 hours of sleep.
So why do I dislike MS for their WP7 so much? It's not UNIX based so security is compromised from the start, it's got a registry that gets overloaded so I've had mobile OS crashes due to that, it's also a DIY job if you need to fix bugs or sort out hardware glitches. iOS and Android both have much more stable bases for mobile computing and while it is a little ad ridden, I have to admit that I save more time per year using either Android or iOS. WP7's flashy interface is just flashy. It's a cover for all the ancient code and buggy features in the device. If you're a tweaker and enjoy tweaking the device to optimal performance, WP7 is for you. If you're tired of tweaking something that just never seems to work right, you're better off with iOS or Android. If you're tired of closing apps down, application freezes, and kernel panics, iOS is the only device out there with that type of experience.
Swipers - Yes, it's those people who incessantly poke around on their capacitive screens who either try to look important or are just bored and need to do something with their hands. Yes, it applies to iOS, WP7, and Android users. These are the people who are normally ADHD or ADD afflicted and have a major problem communicating without fidgeting. They just can't seem to do the powerful things in life and focus on the important interpersonal relationships.