Now that it's generally possible to get a modest discount from resellers (assuming you don't qualify for Apple's own modest educational discount, which usually comes out right around the same), refurbs aren't that great of a deal, but on the other hand every one I've gotten in the past has been functionally indistinguishable from a new one apart from the packaging, so it's also not a terrible deal.
Does anyone know what the source of Apple's refurbs are? They seem like open-box returns, so I've always kind of assumed that's where the vast majority (if not all) come from.