The merry team at ChevronWP7 Labs just announced that, in collaboration with Microsoft, they'll be unlocking Windows phones for a small fee. This creates a wholly legitimate route for developers to access WP7 users. Apple could learn something here.
Windows Phone 7 is "finally" jailbroken! ChevronWP7, the unlocker tool, works with every WP7 phone and allows for the side loading of apps, the use of private APIs, and access to low level functionality. Basically, it unleashes your WP7 phone.