I started my wp8 development by playing around with Cocos2d-x port for wp8. I also used this start by participating to the forum.nokia wiki-competition with my article about Porting Cocos2d-x Games for Windows Phone 8. You can see the port running on the video below. I had really good time with cocos2-x, and I think that I might even make my own game based on this framework. It’s really easy to use, and you can port the games created with it so easily to iOS, and for Android as well.
The source code for tweejump can be found from: TweetJump4wp8