If Democrats win control of at least one house it will mean investigations, hearings, and an end to war profiteering. The initial focus of the hearings will be on profiteering with a keen eye on the Vice President. Democrats will not proceed toward impeaching president Bush without proceeding toward the impeachment of Vice President Cheney first.
This will not be hard. Cheney is dirty and it will be easy to uncover the dirt. He's up to his eyes in bad no bid contracts that put US troops at risk.
If Dems win, Cheney loses.
Now on to the negative side of the equation. If Dems don't win.
Remember, Democrats are going to take the majority of State Houses and Governorships regardless of the national outcome. This is good. But, if Democrats don't win at least one house of Congress there will be a danger of the party collapsing. If a collapse can be avoided the long term prospects for the democratic party will be very very good.
Picture another 2 years of floundering in Iraq resulting in the outright waste of American lives. Picture a Republican Congress failing to do any oversight for another 2 years. The American people will hold Republicans responsible and Democrats will dominate the political landscape in this country for the next 50 years.