I was just reading an article on The Register about this. Pretty intense stuff, the article says these latest Google changes would hit 11.8 per cent of results.

This is interesting too:
But it did compare what sites people chose to block via the extension and what websites its algorithms were identifying as crap sites.

Looking at the top few dozen sites which people chose to block from their search results, the algorithms caught 84 per cent of them, which Google described as "strong independent confirmation of the user benefits".
Which to me says its finally gotten rid of all the crap that comes up in searches that really doesn't give the surfer what they want, but prolly just links to another site (like all those stupid "ask me" or "ask an expert" sites)

This presents a huge opportunity for us to get much better SERPs on our own sites. Conran, I am predicting that you and other content writers will be busy over the next few months :-)