Running an app store is likely not an easy technical task. It is probably made more difficult when you are like Microsoft, who is rumored to be combining the Windows Phone and Windows Stores into one, or at least starting that process. Regardless, when outages happen, it can frustrate consumers. When it happens and goes on for days, you start to tick off developers.
Starting this past weekend, people with existing in-app purchases, aka 'durable IAPs', through various apps like MetroMail and Rudy Huyn's '6' apps are having different levels of success. However, the real issue appears to be for users who pay for a service, like remove ads, only to have the ads comeback, making the usual '99 cent' unlock seem like a fraud.
The problem is not app related, but rather server side with Microsoft and their Store. Developers know this as the 'ANID2 problem' and it has happened before, though this time around it seems particularly frustrating, perhaps due to the larger installed user base.