I suspect, like the Democrats, that Barack Obama at the top of the ticket will help the Democrats make some gains in the State House and State Senate — not enough to take back control, but enough to make gains.
At the end of the day, I think it could be balanced out a bit by Republican gains in some of the remaining North Georgia seats that are held by Democrats. But, I believe that urban Republicans in the metro Atlanta area will have a more difficult time getting re-elected with Obama at the top. I think an Obama candidacy will turn out a large contingent of urban white upper income voters who tend to be liberal, black voters, and gay voters. That will hurt the last remaining GOP legislators in the urban areas around the Perimeter.
At the same time, I think you’ll see increased white middle class voters come out in some North Georgia areas, along with military voters, who will help finally push the last few Democrat seats in the area to the GOP. While the GOP has been fairly fractured with John McCain at the top, by November I’d expect them to be energized.
If Hillary were the nominee, I think the 2006 playing field would be the rule for 2008 in the state house and senate races. At the same time, I think we could see some offset in South Georgia with the rural white male anti-Hillary vote and a suppressed black vote shift the few white Democrat holdouts to the GOP. A Hillary candidacy would also help Rick Goddard in Georgia 8 against Jim Marshall.
All in all, I expect it to be close to a wash this year with little turn over, but I think an Obama candidacy could see the turn over be more substantially in favor of the Democrats. Still, I have this nagging suspicion that Hillary will be the nominee.*
*As Chris notes in the comments I posit that Hillary will be the nominee. Objectively, actually, based on current trends Obama is going to be the nominee. But I just have this nagging suspicion that Hillary is going to do something to take the nomination. I have no rational basis for this suspicion, other than the fact that her last name is Clinton.