I've looked at refinancing, but it's not worth it for us. We refinanced from a 30-yr at 4.25 to a 15-yr at 3.125 about 8 years ago, and since I've been paying a little extra every month, we only have about 5 years left on the mortgage.
That said, I've generally take advantage of every 0% financing offer I can when making larger purchases. Why pay everything up front when I can get a free loan and pay it off over 6 or 12 months?