Charlie Cook thinks Democrats could lose the House in 2010 if they continue their downward spiral. He prefect Democrats will control only 52~54 Senate seats after the 2010 elections. In 2012 and 2014, the math makes it difficult for democrats to feel good about maintaining control of the Senate.
...But if Democrats stay on their current downward trajectory, their majority will be history. The retirements that are likely to result from almost any deterioration in the House Democrats' current situation would reduce their chances of maintaining control to 50-50.