The networks had egg on their respective faces after the 2000 debacle, in which they called states too early, then pulled them, then reannounced them . . . well, you get the point. In light of this, networks claim to have taken a "once bitten, twice shy" approach to declaring election victories this year. Even so, there is a high likelihood that they will error when declaring the outcome in Minnesota.
As I have suggested below, the key factor in Minnesota will be absentee ballots. If the networks assume that the absentee ballots will be within a standard deviation of the outcome from the exit polls, then the networks will most likely be wrong, and may erroneously announce the race. Remember that under the Minnesota Supreme Courts opinion, absentee votes cast for Wellstone count for Wellstone unless the voter casts a subsequent vote for another candidate. Given the limited timeframe for mailing ballots, the majority of these secondary votes will be cast directly at the physical polls, and there is likely to be a large number of individuals who simply fail to do so. This means that the absentee vote should overwhelmingly favor Coleman.
This break in ordinary voting patterns is likely to be forgotten by those handicapping the final outcome of the election, and may lead to a Dewey beats Truman moment for Minnesota.