I think it's probably happened to an extent for a good few years now, but the frequency does seem to be increasing.

There are a lot more reference points now, so we rarely see very underpriced watches there and we do see the same watches over and over again. Still, I would never write it off as a source, every now and again there are still some great watches on there. Particularly on the national version of eBay you link to, I have found ;)