I have a 2.0 GHz Core Duo refurb and it's working great (15 months old, to me). I've bought refurbs in the past and will continue to do so.

One thing to keep in mind, though - the warranty-doubling benefit that some credit cards give you sometimes exclude refurbished products, so keep that in mind and/or give AppleCare an extra thought. I didn't realize this until I was out of my year warranty, so I'm out of luck in this regard. Probably should've sprung for AppleCare on ebay.

Oh well. Fingers crossed I won't need it.

-Chris