As well as the total number of apps submitted (55,044 to be precise), the first week of 2012 saw another numerical milestone for the Marketplace - it was the first week where more than 2,500 applications were published. As we said at the end of 2011, one year to get 40,000 applications, and then 40 days to get the next 10,000. Assuming the rate of submissions stays on the current curve, it's only going to take 25 days to go from 50,000 to 60,000 apps.
These numbers are from our own tracking system, which is also used to power the All About Windows Phone Apps & Games section, where you can browse all of the applications and games, and install them via links to Zune Desktop, the web-based Marketplace, or install them directly by scanning the QR Code with Bing Vision on your smartphone.
If you're interested in getting additional insight or more detailed data, please get in touch and ask about the AAWP App Tracking service.