I visited the p&p homepage on MSDN today, and saw an announcement for a research report by Nucleus Research about patterns & practices, and what companies that use our guidance think the benefits are.  Check out See Real Results With patterns & practices (an overview) and download and read the full report.  As a member of p&p I thought it was informative and showed a few areas that we can improve.  It also showed areas where customers have reaped big benefits from using p&p deliverables, which I would be interested in if I were "out in the real world" and looking to re-use one of the p&p application blocks or an open source alternative.  To borrow a few lines from the report:

"THE BOTTOM LINE
Companies use Microsoft patterns and practices to make their development environments more productive, consistent, and standardized.  Whether used by an independent software vendor, consultancy, or enterprise, patterns and practices can accelerate project cycle times, reduce costs, and shift application development efforts away from code building and toward maximizing business benefits."

-- Guidebook: Microsoft patterns & practices, Nucleus Research Inc., April 2008,
http://www.microsoft.com/downloads/details.aspx?FamilyId=3696068D-BE4A-4731-AB15-492377AA4C6D&displaylang=en

Enjoy.