Not saying it is junk (though I think Obama is down by 5 at the most) but both polls came out of firms that have a record of favoring Republicans and/or have worked with Republicans. I also doubt that McCaskill is down by that much if she is really losing.
Both times Nate Silver released his pollster rankngs Mason-Dixon was ranked quite high (higher than PPP and Rasmussen).
http://www.fivethirtyeight.com/search/label/pollster%20ratings http://fivethirtyeight.blogs.nytimes.com/2010/11/04/rasmussen-polls-were-biased-and-inaccurate-quinnipiac-surveyusa-performed-strongly/ Given that Rasmussen is finding the same thing, I'd feel comfortable saying Romney's probably leading in Missouri by...oh...I'll say 9 points.
I also doubt that McCaskill is down by that much if she is really losing.
Polling from multiple pollsters suggest McCaskill really is losing.
http://www.realclearpolitics.com/epolls/2012/senate/mo/missouri_senate_steelman_vs_mccaskill-1789.html#polls
