Microsoft says that the Store is "surpassing 12 million transactions per day and Windows Phone Store surpassing 200,000 apps". That is definitely good news for both developers and users, and Microsoft has even better news to help get developers excited about the health of the ecosystem. Microsoft is claiming it now has the most carriers connected for carrier billing out of all smartphone platforms, with 51 carriers in 31 markets.
Microsoft is also reiterating a prediction it made last month that was a bit of a reach the first time, and hasn't aged well. Microsoft says that consumers should have $100 million available in their Microsoft accounts to spend on app and in-app purchases. To be clear, Microsoft isn't predicting $100 million in app and game revenue, just that users should have that much available to spend if they so choose.
source: Windows Phone Developer Blog