Insulation being installed in my garage right now. Vapor barrier question?

[gypsyman]

Ok guy is installing right now. I live in northern Califorinia. He says vapor barrier is only needed in very cold climates like Tahoe or Truckee. I am scheduled for dry wall on Wednesday. Guy is licensed contractor. Checked his license on line and no complaints with state of California. Wikipedia and google have me concerned. Is the vapor barrier a must have? Should I install plastic barrier over the fiberglass batts before the dry wall...???