nikon d600 and d800 how many people are happy with them and not happy with them

I have a D800 that I purchased new and haven't had a single problems with.   The guy at the camera store is correct, at least for the D800 (have not yet used a D600 so I cannot speak to QC regarding that camera).  But my D800 has performed above and beyond my expectations.  My previous camera was the 5D Mk II and for stills (and in some ways for video), the D800 is better in every way.  DR and high ISO, AF speed, low-light AF, AF tracking are absolutely amazing.

That said, all new cameras, including the 5D3, can have bugs and minor issues.   I wouldn't let forum chatter deter you from buying any of these cameras including the D600.