I know 17 people who got PS4s from Amazon yesterday and none of them are having any real issues so far beyond typical launch stuff *knock on wood*.
I feel bad for people with issues, Amazon/Sony should have set aside an allocation of systems for potential issues just so the only answer for those people wasn't 'refund', and they could have gotten an exchange from Amazon, ideally a cross shipment situation. Also, Amazon's shipping on mine was crap, the PS4 was sitting in the bottom of the box w/ packing bubbles on top of it, wtf is point if you're not protecting the system box on all sides? I understand they had a ton of these things to ship out, but still.
I don't think we can make any determination of percentage failed at this point. If Amazon shipped out 50,000 units and 500 failed, that's still only 1% of the units overall, admittedly, there will be people with failed units that don't post reviews on their site when it happens, but people with failed units and problems are far more likely to post a review than people who fired up the system and started playing.
Hopefully Sony can take care of the people with issues quickly and by 2014 this is mostly a distant memory.