"Correlation does not mean causation, of course, but the trends do seem clear. Apple opened 123 stores in the U.S. between Sept. 2003 and Sept. 2009 while the Mac's domestic market share grew from just over 3% to as high as 9% (before dipping below 8% last summer)."

"In Western Europe, the effect seems even more dramatic: 33 stores and a market share that grew from as low as 1.5% to more than 5%."

"All this is to support Huberty's contention that China represents Apple's next major geographic growth opportunity, and that Apple's plan to open 25 retail stores in China, announced during its shareholders meeting in February"

I've always felt that a larger Apple retail presence would be beneficial for the Mac in that it would lead to Switchers, a name given to users who have switched from Windows-based PCs to a Mac.  The aforementioned Morgan Stanley report provides some non-scientific insights into how the expanding Apple retail footprint has likely led to impressive market share gains.

You can read the posting in its entirety here.