Advantage over Android is updates!
Amazing how many people on here are saying the same old things about lack of USB mass storage support and so on.
Here's a tip: don't buy it!
Nobody has mentioned the one very big advantage with this platform, Microsoft updates the software via on-air updates. So you're no longer at the mercy of HTC and others to release the upgrades.
Of course, I'm sure you'll not get updates for life. You'll probably still have to get another phone to move between WP7 and whatever is released next. It's not quite as good as Apple who give you about two major upgrades.