After the debates, Bush's share of the vote climbed for a while. Those are people that this poll calls deciding late, who are part of the people deciding in the last month or so. Given that Bush climbed, most of those decisions were for Bush.
But in the last 2 days Kerry's support has been spiking. That is the "late deciders" phenomena, and hopefully will continue to intensify tomorrow. That is the phenomena that people who weren't attracted to either candidate, when the time comes to hold their nose and vote, will vote against the guy whose stink they've had to live with longest.
Cheers,
Ben