Microsoft may not be prepared to deal with the influx of app certifications that have been hitting the marketplace for the last few months, as certification numbers per day have dropped, but app submissions have not. The Microsoft Registered Developer Newsletter recently had this to say:

App Certification and Ingestion Delays

We are aware and are tracking delays in the app certification, ingestion and publishing process. Testing is currently taking 24-48 hours and publishing an additional 24-48 hours. Thank you for your patience as we work to clear the queue and scale to handle the high volume of submissions.

Microsoft is going to have to step up their game if they plan on having higher market penetration, since the more people adopt the operating system, the higher demand for apps there will be which could create a bottleneck.

The current time delays have already discouraged some developers, as the Carbon development team for Windows Phone nearly gave up before getting certified just a few days ago.