One is the social network integration, which sees Microsoft as more outward facing, embracing multiple social networks suck as Facebook and Flickr. Apple has persistently decided to go it alone, even when faced by the whole industry embracing Facebook for example.
The next is the ability to leverage an existing gaming social network in the form of Xbox Live, which has a pretty fanatical following.
Windows Phone 7 will of course still support more form factors that the iPhone, which is likely locked pretty much into its current shape.
Windows Phone 7 also has some new UI paradigms which seem to be catching on pretty nicely.
Are there other advantages I have missed? Let us know below.