Jon Chait, after judiciously conceding that it's possible that "Rasmussen is right and everybody else is wrong," basically makes the case that Rasmussen's polls are, in fact, just right-wing hackery. Their questions are often loaded, they pick odd topics, and even when they poll on ordinary subjects they produce results that are wild outliers compared to everyone else:
Rasmussen polling occupies an odd place in the political culture. In the conservative world, it is the gold standard. If you go to a conservative [site] on basically any random day, you'll see somebody touting a Rasmussen poll.
....The habitual practice by conservative pundits of quoting only Rasmussen polling reinforces conservatives' overweening certainty that they embody public opinion. It's an important component of right-wing epistemic closure, the Republican base having its own pollster who always tells them what they want to hear. In theory, there ought to be a corrective dynamic. If Rasmussen is wrong about the 2010 elections — and, again, you can't be certain he will be — in theory, this would cause Republicans to question their reliance upon his unusual findings. But it's entirely possible that Republicans would simply question the validity of the results themselves. It's massive voter fraud! Obama dirty tricks!
Some time ago I decided to ignore all Zogby polls for everything other than plain-Jane election projections, and over the past year or so I've added Rasmussen to that list. I don't write about them to debunk them, I don't write about them when they happen to produce a result I like, I just treat them as null data. Now, I might be wrong about this. On Zogby in particular, I don't even quite remember what it was that prompted me to put him on my permanent shitlist. But that's where things stand: with the exception of campaign polling, where the questions are straightforward and house effects are generally modest (though rising in Rasmussen's case), I just don't trust either of these outfits.
That said, I think Rasmussen does provide a public service: it gives us some idea of where public opinion will be once Republican talking points enter the civic consciousness. Ask people what they think about financial reform and they'll tell you X. Ask them what they think about, say, financial reform that includes a fund to bail out banks, and they'll say something else. Is that a loaded question? Sure, but that's how Republicans are going to attack it, so it's useful to know what public opinion might be once they start repeating that talking points a few dozen times a day. It's not exactly an accurate reflection of the public mood, but it can still be useful information.