Real Clear Politics has the Presidential race at Obama 313, McCain 158, and Tossup 67, or without tossups, Obama 364, McCain 174. They have the Senate race producing roughly 59 Dems (including Lieberman) and 41 Republicans. Democrats would control a majority in the House, picking up about ten seats, for a margin of about 246 Democrats to 189 Republicans, a 57 seat margin.
While the majority wouldn't be completely filibuster proof, it would shift the balance of power from somewhere in the vicinity of Joe Lieberman, i.e. between Republicans and Democrats with a slight Democratic lean, to roughly the line between the Blue Dog Democrats and the middle of the road Democrats.
Republicans would lose their veto threat option, would require total unity for a filibuster (while still having several moderates left in their caucus), and would have trouble finding the conservative Democratic allies they need to put together majorities on specific issues. Also, in the face of such single party dominance in Congress, it wouldn't be unheard of for a handful of moderate Republicans to defect to the Democratic majority.
Colorado is seen as delivering electoral votes for Obama and a Udall Senate win fairly easily. Markey is actually comfortably leading Musgrave in CO-4 as of the latest reported poll in the race. Of course, if Coffman is elected in CO-6, as everyone expects, Democrats will also pick up the statewide office of Secretary of State, assuring a cleaner election in 2010.
Even if there was a sudden shift to McCain, moreover, it seems likely that McCain might face a stronger Democratic majority in the House and Senate, forcing bipartisan compromise on almost every issue.
RCP is based upon a composite of credible polls of the races, so it is a pretty representative and robust measure. It has a lower margin of error than the polls that go into the mix, probably on the order of +/-2% to +/-3%. Three weeks out, these numbers could actually mean something.
Still, it is hard to believe given Colorado's history, and the nation's political history that we could be seeing such a phenomenal shift. For now, it is nose to the political grindstone until it is really over.
Meanwhile, Canada's snap election today is expected to produce essentially the same results as their last election, returning conservatives to power with a minority government.