Plum Street Studios has an analysis of some of the general trends of absentee voting, which includes early voting. The Conventional Wisdom is that absentee voters tend to be more likely white, older, and more Republican. With the increase of early voting, I think those numbers are less true on the age element, so I believe Democratic absentee voters have increased in recent years, but I think they are still likely to be white voters.
The Enquirer's Greg Korte gives his analysis of the numbers and believes voting trends will hold true from the 2007 election, discounting the younger demographic that turned for the 2008 presidential election. It think it will be clear that the 2008 numbers will not hold up this year and the average age will rise significantly, but I believe it will be lower than in 2007, which I think puts the vote up in the air on a few points. I believe revolves around who the younger African-Americans will vote for, which logic would dictate helps African-American candidates, but I don't see it shaking up the big picture. Maybe 1,000 votes would be in play, something on that scale. 1,000 more votes may swing one candidate up a spot, but unless thats 10th to 9th, it will not make a big difference. It may be the difference between Winburn and Watson getting the open spot.
All of this could be totally wrong and 2008 voter registration movement may carry the voter turnout in the City up from 2007. It goes back to GOTV and in local elections there tends to not be much of that type of effort, so the CW of past elections wins out. We'll have an idea in the morning.