So I just ordered a 27" iMac refurbished from the apple store. I will be upgrading from a 24" 2.4 GHz iMac. Should I be worried about all the returns for yellowing screens, etc of the iMacs? Have they fixed these issues yet? I have my old iMac backed up through time machine. Can I setup the 27" and check for flaws before restoring my time machine backup? Thanks.