The Star Tribune now has a great interactive feature where viewers can look at actual sample challenged ballots (599 posted) , and even vote online on which way they think the vote was intended to go.
[you have to register (free) with the Tribune's website with a username, which is a bit tedious, but no different than most other major online news orgs.]
it's worth it if you're really interested in this race. of the six ballots i looked at so far, there was absolutely no question which way the voter intended to go, with the exception of one ballot. the errors were simply VERY minor technicalities (like a dot was accidently placed in the oval beside one candidate, while the oval beside the intended candidate was clearly and thoroughly filled in; or the way in which an oval was filled in was slightly sketchy).
the one ballot i saw that was the exception showed this: an oval filled in, with an "X" marked over it; the other oval was not filled in at all. that ballot should obviously not be counted at all.
i can't imagine how almost of these ballots could have any questions at all over how their votes were intended; or if they do, that it wouldn't be obvious that the ballot should just be tossed (as in the one i just described).