Refurbs are sometimes not as cheap as you think. Apple doesn't drop the prices enough for me to go with a used as sometimes Macmall or other macsites have them cheaper or close to the same price for a new one. A computer is something I personally wouldn't get used but to each their own.
A refurb isn't a used computer. It's a computer that was faulty, and therefore basically unused, which was then replaced for the original customer, so the faulty hardware is later repaired and sold on by Apple at the discounted price. What you actually get is basically indistinguishable from a brand new Mac.