I expect Edwards already built into the polls to a degree, especially here in NC where the local news has been talking as if he was the choice for the past month.
The only "proof" (the AP/IPSOS poll and the Mason-Dixon NC poll) shows otherwise. That is, they do show a measurable difference when inserting VPs (Edwards and Cheney) into the question. Note also that the AP/IPSOS poll, with its 1% Bush lead without Veeps was in pretty excellent agreement with other polls... showing Bush slightly ahead. So, by all indications, this selection is not factored into any polls. I'm not arguing that any impact will "stick"... esp. for four long months until election day. But, nonetheless, the impact isn't in the current polls.
That's why I say "to a degree". A VP choice can lead to a 5% or so bump. I don't expect to see anything so large. 2-3% in most areas, less in NC and maybe VA.
A smart move on the Kerry campaigns part was to avoid any appearance with Edwards for a while. By making appearing with Vilsack and others it took some of the attention off Edwards, making the obvious pick more of a surprise pick than it is.
I also wonder if it was a good idea to announce so early. This is one of, if not the, earliest announcements of a VP choice in modern times. It usally comes much closer to the convention. It will be interesting to see what Edwards does for the next month and bow the BC campaign responds.
EDIT: One very positive I expect for Kerry is a firming up of his support. I would expect mroe people to be voting for a Kerry/Edwards ticket than they were for a Kerry ticket without a VP.