I've just started the process of returning my Mac Mini, having called to cancel my AppleCare Protection Plan. They said it could take between 4 to 6 weeks to process the cancellation and refund to my credit card (which seems a little lengthy), but as long as it does happen that's all that matters.
I transferred my stuff from the ill-fated Late 2012 Mac Mini to the Late 2011 and was surprised at how well it all worked (I'm familiar with how horrible Microsft's User State Migration Tool is, so I had very low expectations). So once I format/reinstall Mountain Lion on the buggy unit, I'll call to return it and get a refund as well. I hope it also doesn't take 4 to 6 weeks (I recall somebody quite a few pages back saying they got the credit on the day it was received by Apple?). The guy I spoke to said that I could only return it within 14 days and he didn't seem to be aware of the extension until the 7th of January, so I hope I'm not now stuck with two Mac Minis! I would have to take quite a hit trying to sell it. When I click on my order and go to refund it, at least the page still says 7th of January.
Fingers crossed.