I just ordered a refurbished, white 2.2 GHz MacBook, and I am expecting good things. The overwhelming majority of people in these forums and in other Apple circles agree that refurbs are a fantastic value over brand new Macs, and many also believe that machines that have undergone Apple's reportedly strict refurbishment process are more likely to be free of common defects than brand new, off-the-line Macs.
Trust Apple's refurb store for the best deal/value on a Mac. One of the biggest factors here is that all Apple refurbs carry the same Apple warranty as new Macs, something you wouldn't get with even the cheapest "deal" from another source. (Some people even report receiving their Apple refurbs with more RAM or a bigger hard drive than specified on the refurb listing.)