Years ago while I was trying to figure out how to get my first company off the ground I read Guy Kawasaki's book, "The Art of Start". One concept that stuck with me was "preventing the bozo explosion". The theory states that "A" players hire "A+" players, but "B" players hire "C", "C" hire "D", which ultimately leads to a company full of bozos.
Makes sense, but I've always struggled with how to actually do this. The obvious heuristic is to "hire people smarter than you," but sometimes really smart people can be a terrible fit within a company.
It turns out there is a better heuristic: "hire somebody that you would want to work for."
Mark Zuckerburg said this to Paul Graham during an onstage interview at Startup School and it makes a lot of sense. Raw intellect is not the only measure of an effective person; the real trick is finding smart-working people who aren't jerks that get stuff done.
Next time you interview somebody try asking yourself the question, "would I want to work for this person?"