Microsoft will begin upgrading the App Hub's infrastructure this Friday. Upgrades that will add more server capacity to better handle the load increases and streamlining the processes in an effort to speed up the rate in which apps can be submitted, certified and published.

Developers planning on submitting new apps or updates should do so no later than tomorrow. The maintenance work may cause delays in app certification and publication.

The maintenance will also require the App Hub to go offline on Monday, August 6th for about 24 hours (or less). When all is said and done, the maintenance should improve the effectiveness and efficiency of the Marketplace submission and certification process.

We'll be keeping our fingers crossed that all goes well. 

Source: Windowsteamblog