Refurbs are Apple's best deal. These are machines that are returned, for one reason or another, which are then re-inspected by Apple, put in a plain white box and sold for $200 - $300 off list price. Many people on these boards consider them better than new because they are inspected twice. Once initially and then once again after being returned. Of course, any hardware failures will be replaced with new parts. Refurbs show up looking brand new. I have never heard of someone buying a refurb and receiving a unit with cosmetic damage. That is the first thing that is replaced if necessary. I will continue to purchase all of my Macs as refurbs.
Here are two scenarios of how a Mac becomes a refurb.
1. Business X takes delivery of 100 MBPs but realizes they can only use 80 units at this time. They return the additional 20 in their UNOPENED boxes, at which time Apple opens the boxes and inspects them and throws them in the white refurb box and sells them. Whether opened or not, a product that leaves Apple.com/store/etc can no longer be sold as new.
or
2. Joe buys 1 MBP and has hardware or cosmetic problems so he exchanges it for another unit. Apple inspects the machine to figure out why it was returned. If the machine is worth saving, they replace the problem hardware and then sell them refurbished.