Federal Review has some thoughts about those varying poll numbers:
Could it be that pollsters who push "leaners" to answer get better numbers for Bush [while] pollsters who are content to find undecided voters show a closer race? ... I reviewed all polls for the last three weeks and compared the number of undecided voters to the level of support for each of Bush and Kerry.... as undecideds decrease in a poll, both Bush and Kerry's support increases - as you might expect. But Bush's support increases more rapidly....
What does this tell us about undecideds and how they may break? Well, the Republican spin is clear - the undecideds are showing a tendency to break heavily for the President. But the spin you might expect from Democrats is probably more accurate and more relevant to campaigns trying to figure out where the race stands today. "Leaners" are both less solidly behind their candidate and, probably, less likely to vote. Thus, a greater proportion of Bush's voters in the latest polls may be soft.
While that should give some hope to Democrats, they should still be concerned that Bush still holds a lead even when poll victims aren't pressed for whom they lean toward. At the same time, Democrats can hope that this soft support can be turned.
There's an opening for Kerry in this.