Below is a spreadsheet looking at Ohio EV totals, gotten from Cook Political Report's Chris Wasserman.
To break it down: In 2008 early voting in counties that Obama won were 67% of the total, with 33% of early votes coming from counties that voted for McCain. The same ratio in 2012? 64%/36%. BUT! Kerry/Obama counties showed a 10% decrease; Bush/McCain counties showed a 14% increase... and Bush/Obama (which is to say, counties that went for Bush in '04 and Obama in '08) counties showed a .6% increase. We know that absentee ballot requests across the board trended more Republican, so it seems fair to me that we can legitimately at least speculate that Bush/Obama counties are reverting back to the GOP... which means that the blue/red county ratio is much more likely to be closer to 53%/47%.
If true, that is very bad news for Obama, because it means that he cannot hope to rack up the same early voting lead that he had in 2008. Especially since we can't separate out those county votes by partisan ID, yet. When we can I fully expect that the Romney/Obama split to be closer to even (I suspect that Dave Wasserman disagrees with me on that).