There will be another Republican in the Senate to oppose health care reform and any other major progressive legislation. There will no longer be the magical "filibuster-proof" 60 Democrats in the Senate.
The thing is, I don't think it will matter all that much. Any bill the Democrats pass is still going to be as bad as the 41st most conservative (or 60th most progressive) Senator on any given issue. The difference is that that Senator will now be an actual Republican instead of a Republican dressed up like a Democrat.
Others have guessed, and I'm hopeful, that there could be a significant silver lining to this loss. The Democratic leadership in the Senate might just wake up and realize they need to play some hardball, use reconciliation, and pass health care reform and other important legislation with 51 votes. This could lead to a much better health care bill than we would have gotten otherwise. Think of it, the bill would only have to be as bad as the 49th most conservative Senator instead of the 41st most conservative Senator. That removes Lieberman, Nelson, Lincoln, Bayh, Pryor--all the so-called Democrats who helped water down health care reform--from the equation.
I don't know about you, but I'd much rather have a 59-member Democratic caucus with aggressive leadership than a 60-member caucus waiting around for perfect consensus on every issue while Republicans and lobbyists pick away at them.