I guess I have always viewed this behavior as analogous to holding your breath until you turn blue - it doesn't accomplish much in a positive way.
I don't agree with Bush on some things, and I do agree with him on a lot of things. But he is light years closer to my positions than any of the possible Dem replacements. If I decide to make a protest vote, it will be in the primary - in the general election, I am voting for Bush, because any other vote, or not voting, is just a vote for the Dems - as we saw in 1992. I am not willing to put our country through that again, just because Bush doesn't do everything exactly the way I want.
The sources and size of our migration flows are, IMHO, existential questions for our nation.
Also, as noted in my tagline, so far I'm only advocating voting Tancredo in the primary. Will wait and see with the general.