Frankly, more good than harm -- especially for Senate races. Rs correctly identified that they needed Obama, and Ds generally, to fail. Had Ds failed to get anything passed, the Rs could have run on Ds as incompetent wankers who fiddled over big government items and helping "those people" while ignoring the issues that impact "real Americans." Instead, Ds will have a reasonably decent package of things to run on in 2010, whereas Rs are now painted into a corner by their "the sky is falling, it's the end of freedom as we know it" rhetoric.
Nevertheless, Ds still have significant hurdles, particularly in Blue Dog country. The Democratic base, while probably perkier as a result of this and student loan passage, as well as whatever other legislation Congress can get done before recess (I wouldn't entirely count out Don't Ask Don't Tell repeal, as it is very popular with the D base, including some major donors, doesn't face significant corporate opposition, and is mostly a threat to the Blue Dogs who voted no on healthcare anyway and who likely are going down. If Ds are smart (always questionable), they will understand that while this only marginally hurts the seats already in trouble and probably gives their party a boost overall. In the Senate, it hurts Blanche Lincoln, but so what? And it probably helps Boxer.)
I continue to expect to see some significant primary challenges on both the R and the D sides, which will make this season very tough to predict. If Rs go all Tea Party, especially in Senate races, I think Ds do pretty well. If Rs position themselves for the middle, it will depend a great deal on what the progressive wing of the Ds do -- especially after primary challenges. D "get out the vote" is going to be miserable this year. Even with the boost of getting stuff done that will bring traditional liberals who were fed up in August back to the party and the polls, all the enthusiastic young voters and African American voters who turned out for Barack Obama and "change" are likely to stay home. OTOH, the presence of independent Tea Party candidates may be a wild card.
Still, barring anything radically unexpected happening (sudden collapse or improvement in the economy, international crisis, major scandal), I don't think Ds will lose either the House or the Senate. In 2006, I was picking up signals the Rs would lose both houses of Congress even this early, when conventional wisdom held that was impossible. I don't get the same vibe here. OTOH, it's a long way to November.