If he's old enough to remember the late 80s/early 90s, I'd throw out the example George H.W. Bush. Republican voters thought they were getting a rock-ribbed conservative who would continue Reagan's policies of lowering taxes and spending*, but instead they got a guy who raised taxes, raised spending, and appointed David Souter to the Supreme Court.

There were probably some Obama voters who really thought Hope and Change would spread throughout the land and solve all of our problems. I expected Obama to struggle to dig us out of the GWB recession, but I also expected him to at least try to pursue expansionary fiscal and monetary policy, neither of which he seems to be interested in doing. He seems to be trying to convince voters that he's trying for these things but is being thwarted by intransigent Republicans, but at this point, I doubt the sincerity of his commitment to Keynesian economics, the social safety net, organized labor, and basically every other pillar of the Democratic party. Functionally, he's about as right-wing as George H.W. Bush, but at least GHWB tried to put on a Republican face -- Obama seems to be embarrassed and ashamed of any Liberalism that's left in him.

Your Facebook friends are right -- there's some genuine buyer's remorse among the members of Obama's base right now, but the idea that there's an appreciable number of them that would choose McCain/Palin in a do-over is preposterous. Hillary, on the other hand...

*No, Reagan didn't really lower taxes or spending, but Republicans at the time thought he did, and that mythology continues to this day.