Here's some interesting numbers, though just for one county in Ohio.
I queried the data for Hamilton County (Ohio) early voting. Historically, this is a red county that broke for Obama (53% to 46%) in 2008. It is the home to Cincinnati. Out of all the absentee (and early), here's the breakdown of the ballots that have been cast, those still outstanding (unreturned absentee), by party affiliation.
Code:
Pct of Issued Issued Returned Pct Returned
Non Partisan 61.734 71,246 54,088 76
Republican 22.806 26,320 23,804 90
Democratic 15.282 17,637 16,381 93
Libertarian 0.090 104 84 81
Green 0.049 56 45 80
Constitution 0.033 38 34 89
Socialist 0.006 7 5 71
Total 115,408 94,441 82
For comparison, 424,085 votes were cast in 2008.
There are 564,429 registered voters in Hamilton County right now.
I have not found how many early/absentee ballots were cast here in 2008, nor have I found how many registered voters were here in 2008.
Note that in Ohio if you have not ever voted in a primary, you are considered NON PARTISAN. This would include everyone who registered in the last eight months.