In March I bought a refurb 1GHz 17" PowerBook. It ended up having a faulty motherboard. Apple had it for around a month and it always said it was 'On Hold Awaiting Part'. I called them about every other day for 2 weeks and finally talked to customer relations. They offered to send me a free 512MB stick (to double my RAM to 1GB) for my troubles. After 2 more weeks I talked to customer relations again and they stated that they just were not able to get the part yet....so they offered to send my a brand new (not refurbished) upgraded to 1.33GHz 17" PowerBook.
Call Apple and speak with customer relations.....have all of your info about your Mac (what it is, how much $ it cost you, what the problem is, how long they have had it) and make sure they understand you are frustrated but be polite while doing it. Perhaps they will send you a new machine since they cannot get the part in. I believe that someone else in these forums had a similar problem with their new iMac G5 and ended up getting a new machine and a new iPod not too long ago.
Good luck.