Whether "the trend over the last 5 years is that (comparatively) more shops are migrating to the newest version more quickly than before."

Mike, our career services area is placing people in developer/database positions on a regular basis. I get a chance to talk regularly with them, as well as they companies they are working with. And I can tell you that in the last year, the demand for people with some sort of 2008 knowledge/experience is significantly higher than my pretty strong recollections of the industry back in the year after SQL 2005 came out. I also get a chance to talk to people who get placed in jobs and tell me about how their company is also looking at things like Office 2010 and SharePoint 2010 and VS 2010, etc.

Many installations were a bit superstitious about 2005 and elected to stay with 2000. The trend is very different now. I don't speak at as many CodeCamps and User Groups as I used to, but I still do about 15 a year, and can tell you that I've heard far more people over the last year who say their employer/client is more aggressive now about moving to newer versions than they were 3-5 years ago.

So that is my "citation" - satisified? <s>