OK I'll kick off with a little personal experience..
If you have a problem do a thorough search of the discussion forum on the Mac website. I have had the video card replaced twice on my old iBook despite being out of warranty, and on my MacBook I have had the battery charger, cover and battery all replaced free after discovering that they had known problems, this despite all being out of warranty. All info' I gleaned from the discussion forum.
Some years ago I had a software problem (either the mail programme or the address book I forget which), initially the gentleman dealing with my problem actually made things worse, I called back, but part way through the consultation (which wasn't going well) the call was dropped. I called back, and was redirected to a VERY clued up lady in Ireland who solved the problem quicksmart. Now the interesting snippet here was that she said that if you need to make three calls concerning the same problem, you will be redirected to a "level 2" technician who should be more experienced and better placed to solve your problem.