Let's stop being abstract and start being specific.
I think recent polls show Democrats will get a slim majority of the House. Lot of Republican districts have all of a sudden become competitive, such as Foley's, Boehner's, Schmidt (Ohio) etc..etc... and the Foley scandal and the Iraq War will be the end of Republican majority.
However, Senate I think will stay in Republican hands or at best be tied with Dems.
Tennessee - I hope Ford wins, but I'm a little skeptical voters will vote for the more aggressive, yet better candidate than the lackluster yet 'safe' candidate which is Bob Corker. The racial element in the election will still be significant. Tennessee has a very popular Democratic governor who has an approval rating of 65 percent (amazing). I don't know if that's enough for people to overlook the racist and negative campaigning that has been going against Ford.
VA - Allen is hitting back hard suggesting that Webb disrespects women and children. Allen's campaign has lifted passages from a bestselling FICTIONAL novel written by Webb which includes scenes of a war veteran witnessing incest, rape, and homosexual acts. I have a feeling this is going to get front page coverage until the election and will overshadow Allen's racist past.
Missouri I think Democrats can take, although it will be close. The attack on the Michael J Fox ad will blow up on Republicans. Missouri is a purple state that tends to represent the general mood of the country, and that I think gives the Democratic challenger some advantage.
Democrats will keep New Jersey, despite Menendez' poor performance in the polls. NJ is a Democratic state...yes the Democrats have a 'corruption' problem due to their monopoly on the state, but this isn't the year for Republicans to get that seat. The Republican has a famous last name, but I don't think that's enough. NJ is a blue state as they come.
Democrats will get Montana due to Conrad Burns list of embarrassment and having a strong, natural, outsider opponent. Democrats will sweep in Ohio due to the Republican incompetence and corruption. Democrats will keep Maryland. Democrats will get Pennsylvania and Santorum is finished. I don't know if I forgot any other close U.S Senate races.