I'm a Minnesota voter and we figured this was coming for at least a couple years. As a candidate, he can't be under estimated, he's educated, interested and informed. I doubt I'll vote for him if he is the candidate, but I respect him and think he is a bona fide candidate who can debate the issues with the best of them. He's going to have some stiff competition to get the party's nomination, but I think he's the guy to beat rigth now.
Franken seems to really have it in for the Senator he's running against, Coleman (R). We had an open seat in MN this last fall and he didn't run, I think he wanted to wait and go head to head with Coleman. Another Minnesotan that can't stand Coleman is Garrison Keillor, but that's another story. Personally, I voted for Coleman and likely will again.
We learned in 1998 when Jesse Ventura was elected that you can't underestimate anybody, especially when they have name recognition.