From Public Policy Polling, which usually surveys for Democrats:
Several Florida Senate polls conducted shortly after Connie Mack IV's entry into the race found a toss up contest, but PPP's newest look finds that any announcement bump Mack may have received has now receded. Bill Nelson leads him by a 46-35 margin. That's pretty consistent with two earlier polls of a Nelson/Mack match that PPP had conducted. In March we found Nelson with a 13 point advantage and last December we found him ahead by 9 points.
Nelson has two big things going for him in a match against Mack. One is that he wins 14% of the Republican vote, an unusual amount of crossover support for a Democrat. The other is that he has a 42/33 advantage with independent voters. 22% of Republicans are undecided compared to only 13% of Democrats so this race will likely tighten up once the GOP unites around a candidate, but for now Nelson has a healthy lead.
Nelson's approval numbers continue to be tepid with only 38% of voters approving of him to 37% who disapprove. But as we've explained repeatedly, Nelson's numbers are a little bit misleading. The reason they're so low is that only 51% of Democrats approve of him to 27% who disapprove, an unusually weak standing for a Senator to have with the party base. But even though only 51% approve of Nelson, 76-80% say that they will vote for him in a general election. Barack Obama will have to provide the enthusiasm for those folks to get out to the polls, but once they get there they'll vote for Nelson too. Although Nelson's unusually weak with his own party, he's on positive ground with independents at 40/35 and also gets good marks from a higher than normal 22% of Republicans.