Nate Cohn analyzes them. He notes that one reason "Romney performs well in national polls of early voters is the composition of the states with substantial early voting":
Many of the large, Democratic-leaning states in the northeast and Midwest, like New York, New Jersey, Massachusetts, Pennsylvania, Minnesota, and Michigan don’t permit in-person early voting.
Illinois now allows in-person early voting, but the state still prefers to vote on Election Day, as just 10 percent voted early in 2008. The only blue states with more than 10 electoral votes casting an above average share of their votes in early voting were Washington and California. In contrast, the three largest red states of Georgia, Texas, and Tennessee each cast an above average share of their ballots early. So far in 2012, each of those states has reported higher early voting turnout than California or Washington, where millions of ballots will be cast by mail. As a result, "red states" are beating "blue states" in early voting by an 8.5 million to 4.9 million vote, according to figures taken [Wednesday] from Michael McDonald's indispensable site on early voting.