I calculated this for states that held Senate elections in 2010 by using state PVIs here.
Those were just the counties closest to the statewide average for one election. Alpine, Calfiornia certainly fails as a bellwether long term.
I used PVIs, so it's the counties closest to the statewide average over the past two Presidential elections, not just 2008. By definition, that shows recent trends, not long-term trends. Alpine, California was a decent bellwether for recent Presidential elections - as good as Santa Barbara and Imperial and slightly better than San Benito, which was pretty decent, too.
