There's a lot of noise about Arlen Spector's move to the Dems, which along with Al Franken (when he finally gets there, probably some time in 2011) makes for 60 democratic Senators.
But 60 democratic senators, while it sounds filibuster-proof, is nothing of the kind.
If the democrats try to rely on those 60 votes, where does the power lay? With the right-leaning democrats. It hands blue dogs the ability to bring on a Republican filibuster any time they have an issue that they want their own way on... and I don't imagine they won't use it a few times.
They can't do it *every* time, but that doesn't mean that they can't do it at all. If there's something they *really* want, you can bet that's a bargaining chip they know they hold. Even if they don't actually use it, the threat may be enough to get them what they want at the bargaining table.
Let's wait and see how it all pans out.