Unfortunately, it seems that threads like this only attract those who have had a bad experience with their copy of the lens. Mine is about two months old and I've shot my best landscapes with it, no issues whatsoever. I think you will find that the "silent-but-happy" owners probably far outweigh those unsatisfied with their copy. I think the takeaway here is that you should buy your lens from someone who will take it back when you're not happy with it ... but that is true for any expensive gear you buy.
That said, this particular lens *does* seem to have a less-than-stellar quality control reputation ... I might not be buying one "as-is" off of ebay in the coming years.
Regards,
germar