The Windows Phone Marketplace just reached a major milestone as now more than 50,000 apps have been submitted to it. While the numbers are nowhere near the two OS giants of the industry, there are lots of positive signs of optimism for WP7.Particularly, the growth of apps has been really accelerating since the launch of the Nokia Lumia line of Windows Phones. The first 40,000 apps took over an year while the last 10,000 has taken only 40 days. It truly suggests that the marketing push by Nokia and Microsoft has done the trick for the still budding OS, they have succeeded in attracting developers to the platform. Overall its a truly positive achievement and promises some good times for Windows Phone in 2012.