odiv

And people just started doing this mid-November 2012? Or Google only really started taking it into account then?

A lot of people have been giving earnest, authoritative sounding SEO advice, but I don't think anyone really knows except Google.

Looks like it was November 17th according to this: http://searchengineland.com/metafilter-penalized-google-1921...

Any additional insight based on that date?

Full disclosure: MetaFilter member reading about this stuff everywhere with interest who joined here to comment. HN seems right up my alley with the simple design though I'm not sure if I'm ever going to be a threaded comments kind of guy.