McClatchy/Marist, Oct. 1, 2010 (.pdf)
The Milwaukee Journal-Sentinel's Don Walker blew it here: his 52% to 45% figures are taken from the responses of likely voters, whose sample size was 506 respondents with a margin of error of +/-4.5%.
Too small, and too wide.
Among registered voters (Sample = 806, MOE +/-3.5%) it's Ron Johnson 45%, Russ Feingold 43%, with 11% undecided. Expect to hear little triumphalism from the Ron Johnson faithful over this poll.
Yet do expect from Ron Johnson a lot more ahistorical teevee ads, comically incoherent "principles," and feverish backpedaling.