I know a prediction that only has the Democrats picking up one seat goes against conventional wisdom but that's all I see right now. There are a number of states (e.g. Pennsylvania, Michigan, Ohio) where Republicans made big gains in 2010 and control redistricting. The redistricting will help but I think Republicans will lose seats in such states. There are just too many vulnerable reps.
That'll be balanced out by gains in Georgia, North Carolina, and Texas. I don't see big losses in Illinois or California, but even if the GOP loses 6 seats more than I have them losing that's still only a 7 seat Democratic swing. It's possible that environment and further redistricting will sway my prediction more Democratic, but I doubt it'll approach anything near 15 seats, let alone the 24 they now need.