With the Democrats holding California and Nevada, they are certain to retain the majority position in the Senate. They may add to that if Patty Murray can hang on in Washington, though she was trailing the challenger at last count.
That doesn't mean that the Senate will necessarily remain in Democratic hands for much longer.
If the Dems have a bare majority with VP Biden spending a lot of time in the Senate to break ties, I have to wonder if some Democrat Senators might not switch parties. Why? 2012. There are several Democrat Senators from heartland and mountain states who will be up for re-election in 2012. It may be that a couple of them will not want to run with the President and may not be able to run from him. They may be looking at the results tonight and thinking that their political survival may require a change in approach and label. They may switch parties. No, that isn't a scenario we should expect in California or New York. But places like Montana, Nebraska, and New Mexico may see that kind of thing happen. And does anyone remember Joe Lieberman? I don't think he'll switch parties, but there are others who might, others far more electorally vulnerable. This has happened before - Shelby and Night Horse Campbell moving from the Dems to the GOP and Specter moving from the GOP to the Dems.
The count in some of these elections may go on for awhile - and so might the drama. Colorado, Alaska, and Washington are too close to call, though the Alaska outcome is a choice between two GOP candidates. If current form holds the Dems will have 51 seats, with the new West Virginia Senator voting with the Republicans on economic issues and the independent wild card Lieberman ready to unsettle things even further.
My guess is that the GOP would like to see the Senate stay Democrat for two more years so they have two 'targets' for their campaign in 2012. They may not have that luxury.