Found this on why Dems shouldn't get their hopes up based on voter turnout:
High Democratic Turnout Sends a Mixed Signal for November - Yahoo! News
It seems like the only two times the Republicans have had a higher turnout than Democrats in the last 36 years have been 2000 (where they did lose the popular vote) and 1996 when Bill Clinton ran unopposed on the Democrat side. So we probably cannot infer too much from those numbers. The bigger worry for McCain is how much money Obama is raking in.