I'l give my two cents here as I am an Android user that purchased a WP7 phone to see if I could make the switch. I love Microsoft products. I love my Xbox 360, my original Zune, my Zune HD, Windows 7, I loved my Samsung Blackjack, etc. I am a Microsoft ******.
Having said that, there is no way I can leave Android behind. It does absolutely everything I need it to do for work and personal use. I want to use WP7 so bad but I just can't. I NEED multitasking. I go in and out of apps and need to copy/paste between them frequently. Android's notification bar is second to none. It is so nice having a dropdown with all of my notifications right there. Push notifications for any app. Flash. I can go on and on. In my opinion an HTC Sense device is the best Android device if you need it for work and personal use. I have a Droid Incredible. Sense handles my Exchange account perfectly. The email is laid out well, I see all HTML email, my calendar and contacts sync perfectly, etc.When I tried WP7 for a few days it was a huge step back. I was more functional with my Blackberry unfortunately.
If WP7 ever gets all of it's shortcomings figured out I may take a look again but in my opinion it was inexcusable to release it without some of these important features. It seems like if you currently have an iPhone, Android, or even a Blackberry switching to WP7 right now would be moving backwards. If you're coming from a feature phone then it would be an upgrade. Yes the Xbox Live stuff is awesome, but I need a multitasking phone for what I do. I'm sure a lot of people don't need a phone for what I do and for them maybe WP7 is just what they need. Just wanted to give my opinion since I tried to make the switch.