Since the Clinton campaign is gong to be pushing hard on the "popular vote" argument for the next 48 hours, I thought I'd link to this analysis that I conducted several weeks ago.
Bottom line: the Clinton calculation of the popular vote in Michigan nets her campaign 328,151. However, based on the exit polls, it is safe to say that this is not an accurate reflection of her support among Michigan voters. Instead, that margin is something more along the lines of 65,000.
Here are the key passages:
Of the 593,837 Democrats who turned out to vote in the Michigan primary, 55% (328,151) cast their vote for Clinton. But what would have happened if all the candidates' names had been on the ballot? Fortunately, we have exit polls from Michigan which can give us some insight here. On the exit poll survey, voters were asked who they would have voted for had every candidate's name actually been on the ballot. Here are the results:
So, what happens if re-allocate the Michigan vote accordingly? In Michigan, the vote would have broken down as follows:
Clinton: 273,165 votes
Obama: 207,843 votes
Edwards: 71,260 votes
Thus, had Obama's name been on the ballot, Clinton's margin in the state would have been much smaller. Of course, there is no really good metric for measuring the vote in Michigan. Even in this scenario we have to assume that turnout wasn't suppressed by the fact that Obama's name wasn't on the ballot. Yet, you can imagine that many Obama supporters (and some Clinton supporters) may not have bothered to turn out to vote given that they knew that their votes were not likely to count. Nevertheless, this metric probably comes closest to capturing the actual preferences of those who did turn out to vote in Michigan.
UPDATE: This post from Mark Blumenthal regarding the accuracy of the exit polls for making such judgments is definitely worth a read.