This is becoming a pretty old story (Alan Abramowitz wrote about it definitively last year, as did John Sides), but since it hasn’t much sunk in amongst mainstream media political observers, its worth repeating ad infinitum: Mark Blumenthal makes the case that most “independent” voters aren’t very independent. The general consensus is that of the 30% to 40% or so of Americans who call themselves independents, no more than ten percent are independent voters in any meaningful sense of the term. And “pure independents” are also less likely to vote than partisans.
This is important for a whole lot of reasons. For one thing, the idea that “independents” are a third force in politics positioned in some moderate, bipartisan space equidistant from the two parties is entirely wrong. They are not a bloc of voters who think just like David Broder or David Brooks, spending their days pining for deficit reduction and “civility.”
More immediately, the high percentage of Tea Party activists who call themselves “independents” obscures the fact that most of them are in fact highly partisan Republicans who are close ideologically to the right wing of the GOP. Here’s how Blumenthal puts it:

Remember the 52 percent of Tea Party activists who [in a recent CNN poll] initially identify as independent? It turns out that virtually all of them lean Republican. According to CNN, 88 percent of the activists identify or lean Republican, 6 percent identify or lean Democratic and only 5 percent fall into the pure independent category.
Remember that CNN pollster Holland reported that 87 percent of the Tea Party activists would vote Republican if there were no Tea Party-endorsed third-party candidate running? That makes perfect sense for a group that is 88 percent Republican.

Why do functionally partisan, and sometimes quite ideological, people self-identify as independents in such large numbers? Some of it is just fashion: many folk conflate “independence” with “intelligence” or “thoughtfulness.” Some of it reflects short-cuts by pollsters, who often give respondents the impression that voters who have ever split a ticket should call themselves “independents.” In the case of the Tea Party activists, there is undoubtedly some mistrust of the godless moderate “GOP establishment” and its Beltway habits–mistrust that will not, however, keep them from voting uniformly for Republican candidates in any two-party contest, and which in any event may not last long given the rightwards trajectory of the party as a whole.
In any analysis, wherever possible “independents” should be broken down into D and R leaners and “true” independents, and the vast array of “independent” ideological tendencies should be explained. Better yet, pollsters should ask follow-up questions to determine actual voting behavior and specific views rather than self-identification by partisan or ideological labels. Otherwise, we’re allowing those labels to distort reality in major ways.