David Corn has up a nice post about Durbin's explainationof the filibuster compromise.
Bottom line, it's hardly a cause to celebrate and may blow up at any moment, but in the end, the Ds could not get the votes to keep from being nuked. So, it was time to make a deal.
It's an interesting read. As I've written about here, the pressure on the Rs to come through on this was huge.