You can see the recent polling here.
I'm hoping Hovde wins on the GOP side, not just because most polls have him running a little weaker against Baldwin, but because he's more likely to collapse in the general election under gaffes or scandals. He's less experienced at politics, and has said some ill-advised things so far in the campaign. I'd estimate a higher probability of his having currently undiscovered skeletons in his closet.
I'm checking the Wisconsin Senate polls pretty frequently these days, and it usually comes out disappointing because nobody has reported a poll of the Republican primary for the last 3 weeks. With the primary election to be held on August 14, that's a weirdly long polling drought. What we do have recently is a small (500 voter) Rasmussen poll in which Tammy Baldwin leads all GOP candidates by margins between 3 (Eric Hovde) and 7 (Tommy Thompson). Again, I think Hovde is still the candidate I want to go up against, since most of the polling goes the other way and Hovde has more downside. But in any event it's a nice result.
Anyway, this is one of the races that I'm thinking about opening up my wallet for. Baldwin will be a reliable Democratic vote on everything and a force to move the party leftward. She seems to be pretty good at avoiding trouble, and since she's only 50, she could occupy the seat for a long time.