The last faithless elector was in 2000 where Barbara Lett-Simmons, representing Washington, D.C. abstained in her vote for president as a protest for the lack of Congressional representation for D.C.
If it had been important, she would have voted for Gore, but in the end, the final tally was 271-266 and one abstention.
Electors are appointed by parties based on their loyalty and activism for the party. They don't just appoint anyone, so the odds of a faithless elector throwing an election is pretty much zero.
Back in the old days, a lot of negotiations went on and vote after vote of the electors would happen. These electors were not tied to any one candidate, so they were free to elect anyone.
In 1788 and 1792, the vote was unanimous for Washington, but not after that. John Adams in 1796 barely squeaked out a majority against Thomas Jefferson, his old friend and adversary by 71-68. In the rematch in 1800, Adams placed third after Jefferson and Aaron Burr.
