I'm especially glad that the Democrats have control of Congress because I'm hoping it means they'll use their power to investigate the Bush administration's conduct, especially in regards to the Iraq War. But it might not matter if they do investigate:

It is worth reminding ourselves -- as the Vice President just made quite clear again-- that the pathological individuals who occupy the White House do not recognize the power of the law or the power of the courts to limit what they can do. Therefore, the fact that Democrats now control the Congress will be of little concern to them, because the most the Democrats can do is enact little laws or issue cute, little Subpoenas --- but, as the Vice President just said, they think that nothing can "tie the hands of the President of the United States in the conduct of a war." And he means that.
G. Greenwald

Something I don't quite understand is why Nancy Pelosi has said that impeachment is off the table. Why would you want to take that option off the table? But I don't understand exactly how impeachment works, so maybe that's my problem.