According to a report from Asymco, the App Store is on the verge of hitting 400,000 submitted iOS apps. At this time, over 390,000 apps have been uploaded to Apple, with a reportedly 1,000 new titles submitted per day since 2008!
The report also notes that Apple has not reached 400,000 in sales, as 65,000 apps are no longer active in the App Store. This could be the result of Apple or the developer removing apps.
Using additional information from 148apps, December seems to be the most popular month for submitted iOS applications. December 2008 saw 3,868 apps submitted, which was followed by 25,517 app submissions in December 2009, and most recently December 2010 saw 25,429 app submissions.
Based on these estimates, Apple may achieve another major milestone of 500,000 submitted iOS apps by mid-2011.