Gareth,

in 2000, a DC elector abstained to protest DC's non-statehood.

in 1988, one delegate voted for Bentsen for president and Dukakis for VP instead of the other way around!

in 1976 a Washington Republican voted for Reagan/Dole instead of Ford/Dole

in 1972 a Republican elector voted for two libertarians, making one of them the first woman to receive an electoral college vote.

etc, etc. It has happened 156 times in American history, but many have been because of the death of the original candidate.

None of these so-called "faithless electors" has ever affected the outcome of an election.