Dems don't need to control 2/3, just half, to make the huge difference they need to. They're going to be passing very reasonable legislation that shouldn't have too much trouble getting bipartisan support.
The important thing about a Dem majority is that now they get to chair the committees and set the agenda. That means they'll be working on health care, education, the environment, lobbying reform, and other actual consequential issues on which the Dems shouldn't have too much trouble finding a dozen Republicans to go along. It also means they can start investigations to root out incompetence and cronyism in the executive branch, especially the defense department, which has been so far protected by the Republicans. Our troops were sent into Iraq unprepared and with a shitty plan, and now the people responsible are finally going to answer for it, starting with Rumsfeld. There were no checks and balances under the Republicans, and now there will be.
The fact that some of the new Dems are socially conservative won't matter, because the retarded social wedge issues like gay marriage, abortion bans, and flag burning aren't even going to come to the table under a Dem legislature. The Dem priorities are more significant than their positions.
This is a very good thing.