I think there's something to the theory that there are some candidates so vile that even the supporters won't admit it to a pollster. This happened in 1984 with Jesse Helms. Hunt was ahead in the polls and ended up losing fairly handily, actually.
Helms had Reagan's coattails to help pull him through as well. It was a very good year for the GOP nationally; this year is going to be an excellent Democratic year.
If Burns does pull it off it would probably be the biggest comeback win since Helms in 1984.
If 1984 had been a 2006 like environment, there is no way Helms would've won.
I would look more at the Helm's 1990 and 1996 analogy. Gann suffered from the Tom Bradley effect as well, but this one it seems Burns is gaining momentum.. RealClear Politics agrees.
http://www.realclearpolitics.com/epolls/2006/senate/mt/montana_senate_race-11.html