David Broder today argues that the rise in self-identified conservatives is a big problem for Democrats:

Sometimes the most important clues are hiding in plain view. That was the case in late June, when the Gallup Organization reported that the share of voters who describe themselves as conservative had increased from 37 percent to 42 percent in the past two years.
That does not sound like a big change. But given the long-term stability of basic philosophical alignments, the reaction it measured to the economic troubles and the performance of the new Democratic administration is very significant.

Hmm. The trouble here is that ideological self-identification is a pretty shaky measure of what voters believe, and the numbers bounce around without much correlation to real-world changed. Here's Gallup's historical chart of ideological self-identification:

This doesn't seem to tell us much about political performance in any given year, does it? James Downie created a handy chart comparing the Republican Party share of the two-party vote, on the left, with the percentage of the electorate self-identifying as conservative, along the bottom:

Not much correlation there. Now, it's clear Republicans are going to gain a lot of seats in 2010, but there's not much evidence that the rise of self-identifying conservatives has anything to do with it.