DailyKos founder Markos Moulitsas has admitted that some or all of the surveys the site conducted through Research 2000 may be faulty — even fabricated:

I have just published a report by three statistics wizards showing, quite convincingly, that the weekly Research 2000 State of the Nation poll we ran the past year and a half was likely bunk.
Since the moment Mark Grebner, Michael Weissman, and Jonathan Weissman approached me, I took their concerns seriously and cooperated fully with their investigation. I also offered to run the results on Daily Kos provided that they 1) fully documented each claim in detail, 2) got that documentation peer reviewed by disinterested third parties, and 3) gave Research 2000 an opportunity to respond. By the end of last week, they had accomplished the first two items on that list. I held publication of the report until today, because I didn’t want to partake in a cliche Friday Bad News Dump. This is serious business, and I wasn’t going to bury it over a weekend.
We contracted with Research 2000 to conduct polling and to provide us with the results of their surveys. Based on the report of the statisticians, it’s clear that we did not get what we paid for. We were defrauded by Research 2000, and while we don’t know if some or all of the data was fabricated or manipulated beyond recognition, we know we can’t trust it. Meanwhile, Research 2000 has refused to offer any explanation. Early in this process, I asked for and they offered to provide us with their raw data for independent analysis — which could potentially exculpate them. That was two weeks ago, and despite repeated promises to provide us that data, Research 2000 ultimately refused to do so. At one point, they claimed they couldn’t deliver them because their computers were down and they had to work out of a Kinkos office. Research 2000 was delivered a copy of the report early Monday morning, and though they quickly responded and promised a full response, once again the authors of the report heard nothing more.
While the investigation didn’t look at all of Research 2000 polling conducted for us, fact is I no longer have any confidence in any of it, and neither should anyone else. I ask that all poll tracking sites remove any Research 2000 polls commissioned by us from their databases. I hereby renounce any post we’ve written based exclusively on Research 2000 polling.

By the way, based on a quick search of the site, the term “Research 2000″ appears in a total of 716 DailyKos posts.