John wrote to tell me that a prominent political blogger, Kos, has said that this poll is conducted on the internet and should be taken with a huge grain of salt. You can register yourself here. Further research turned up this note from MSNBC on the phenomenon of online polling, and I note that Harris also has an "interactive" (code for online) polling system as well.
Finally, I read the background on their method at the Zogby site, and found that this, the first in a series of polls on battleground states for the 2004 presidential elections, reflects a qualitative improvement over previously done online polling efforts (which they've been doing since 1998):
How about the issue of how representative internet polls are? First, let’s understand that what we are doing at Zogby Interactive is very different than simply posting a question of the day and asking people to vote. Instead, we have spent the past six years collecting tens of thousands of email addresses, complete with demographic, behavioral, geographic, and attitudinal data on each person who has registered to be part of our internet surveys. We send an email to a sampling of tens of thousands of these addresses and invite them to visit a secure website to complete a poll. Each individual receives a secure link. These emails have been updated, cleaned, and validated over and over through the years. We have been testing many of our interactive surveys against our telephone surveys and have found growing correspondence – actually, in most cases, within 1 percent – between the results. In addition, we have been using our telephone call center to validate a sampling of our interactive respondents to ensure that they are who they say they are.There's more, but in short it sounds like something we should not automatically rule out.
Another interesting tidbit is that Zogby did a poll last year in Iraq, the results of which were twisted by (surprise, surprise) VP Dick Cheney. I found this op-ed in the Guardian from last year, written by another Zogby, the brother of polling founder John Zogby, James, who's president of the Arab American Institute, who took Cheney to task (no, the Iraqis are not really happy with the US presence, Dick...)