[IMRight]

Mason-Dixon has a good reputation among political professionals

That's actually underselling it. M-D is hands-down the best state-level polling organization in the nation. There are some individual states that may have local firms with a better record, but none of the big players (Zogby, Pew, Gallup, Rasmussen, etc) are as reliable as M-D.

[concerned about politics]

Wall Street (Barron's) predicts holding the house by 1 and losing 2 in the Senate. If that's it, it's a huge win for the good guys. These are mid terms. It would be an unprecedented win for Republicans.