The company has seen 1.5 million downloads of its Windows Phone Developer Tools. 36,000 developers have paid to become members of the AppHub, and 1,200 are registering every week. The Windows Phone 7 platform seems to be providing developers with a decent revenue stream, as over 65 percent (7,500 in total) are pay-for apps. Of these available apps, 1,100 of them are using Microsoft's built-in Advertising Ad Control platform to generate revenue.
Microsoft has surpassed 11,500 apps on the Windows Phone Marketplace, which is a drop in the bucket compared to the six digits of apps that iOS and Android have. Still, the company was able to reach the 10,000 apps milestone quicker than any another mobile smartphone platform. Windows Phone 7 owners are downloading an average of 12 apps a month, and Microsoft says its certification process takes an average of 1.8 days. 62 percent of apps are certified on the first attempt.
For more details on all the numbers, check out A Year Later–The Windows Phone 7 Numbers That Matter on The Windows Phone Developer Blog. Warning: it's a very verbose post.