One way to get a sense of what turnout may look like is to look at what the early voting figures look like. The Texas Secretary of State made available data on how many people voted early in Texas's 15 most populated counties. While this is merely a snapshot of the state as a whole, it is still worth looking at. Therefore, I have appended turnout data from the 2004 Democratic presidential primary in Texas and census data on the percentage of each county's population that is black, Hispanic, and white. These figures are below (the early voting numbers are just those voting in the Democratic Primary...Republican primary voters are not included):
The key column here is the fourth one, which presents the early voting in 2008 as a percentage of turnout in 2004. The first striking thing here is the great increase in turnout in 2008. In Denton County, six times as many people have voted early in 2008 as voted at all in 2004. Most people estimate that early voters will comprise one-third of the electorate in 2008, just to give a sense of how much turnout will be up throughout the state in 2008.
More importantly for understanding what the electorate might look like is comparing the percentage increase in turnout with the racial and ethnic data. Interestingly, it looks like early voting is greatest in the counties that have the highest percentage of non-Hispanic whites. Whites have split relatively evenly in primaries up to this point, so this may not strongly advantage either candidate.
Fort Bend County sticks out in this analysis because it is the county (among these 15 most populated counties) with the highest percentage of African Americans. Early voting in Fort Bend is over 3 times greater than overall turnout in 2004, and given Obama's edge among African Americans, this should benefit him.
Interestingly, the counties with the largest Hispanic populations have seen the lowest amount of early voting.
Of course some types of voters may be more likely to vote on election day rather than cast their ballots early, so it is important not to draw too much from this data. But, based on early voting, we may see turnout increase more among African American voters than it does among Hispanics. If that is the case, then it should benefit Obama. Of course, we will soon know not just what the electorate looks like, but which candidate that electorate favored.