Unless you have been living under a rock, you'd probably heard of HowardForums.com. This excellent mobile phone/carrier related user community has just released a WP7 app. It employs the familiar metro UI throughout the app, push notification (guess this is for forum messages - you need to log into to your howardforums account, don't think you can just create one from the wp7 app but you can go to the main website to register for an account). It supports forum posting and from what I can tell, its pretty slick looking. You can create/reply to posts and etc.
It did, however, crashed on me a couple of times for no reason.