Recently I was looking into the in-app purchases for Windows 8, and I was dismayed to discover that the articles on MSDN about it were completely inaccurate. I was only able to learn what I needed to because there was some sample code that I was able to work backwards from. While I was able to get my work done, it was a frustrating experience. I remember going through this with Windows Phone 7 as well.
Justin James is the Lead Architect for Conigent.