There is a case to be made for conservatives to not support John McCain. I don't agree with that argument -- but it is a legitimate one. There's also an argument to be made for libertarian-leaning conservatives to support Bob Barr.
However, any "conservative" who legitimately supports Obama for president has, as far as I'm concerned, disqualified himself as a conservative. Nobody who truly takes the concepts of free enterprise, the right to life, or strong national security seriously, would entertain such a thought.
These so-called conservatives are really folks who value eloquence over substance -- or who are caught up in the "cult of youth".