Sheridan,
I have, and have had many scopes and from many manufacturers - including Burris. I have seen (with my own eyes - not something I read in a magazine or online) at least a half dozen Burris failures. These were not failures on the rifle range, or in the whitetail woods, but failures of scopes attached to hunting rifles on elk and mule deer hunts from spike camps in the Rocky Mountains. It was certainly not 100% of the scopes that failed, but that is a high failure rate considering that losing your scope back in the boonies may well ruin your hunt. Thankfully there was usually someone that had tagged and was willing to lend a rifle to the poor soul. I can remember one guy gut shot a 5x5 that was never recovered after the rifle shifted the POI by about a foot at 100 yards.
I have also seen cheap scopes (not Burris) fail, usually fogging up. The Burris scopes were fairly expensive models and each of them had a problem with the crosshairs moving or coming loose but none of them fogged.
These incidents were a few years ago, and I have not been seeing very many of these scopes in camp lately. Burris has hopefully done a better job and is making a better product.
Extensive testing? The best test possible - actual hunting conditions. Lemon? This was not a "one in a thousand" problem.