I'll leave most of this talk to the smart political science types, but it's worth noting that Pennsylvania, New York, Rhode Island, and Mass. are all blue states which have an annoying tendency to elect Republicans to statewide office. In PA that changed with the election (and re-election) of Rendell and now Bob Casey in the Senate. In New York, say hello to Governor Spitzer. In Mass., say hello to Governor Patrick. In RI, say hello to Senator Whitehouse.
With respect to the Senate gains especially it's hard to not to see those gains as pretty permanent. Barring scandal, those are two seats that will remain blue for a very long time.
