His model explains elections since 1960 with an average forecast error of only 2.4 percent — far better than any conventional predictions derived from polling.
The only election he really blew was in 1992, when Bill Clinton beat George H. W. Bush. If you take that one out, his record shows only a 1.6 percent average error. He even correctly called the squeaker in 2000 with Gore marginally winning the popular vote, when all the traditional polls were calling for George W. Bush to win the popular vote handily.
This article about him is pretty good (though I certainly don't condone or support the other stuff on his site). For more fun with numbers, check out his prediction site.