The solution is to log out. For those of you who like being signed into Gmail put "accounts.youtube.com" in your adblock filters. That will prevent Google from automatically signing you in to Youtube and other services.
Now, I don't know that they do that, but they certainly have the technical means to do so.
He mentions they use ~30 points of info to identify you, even if you're logged out.
> Even if you're logged out, one engineer told me, there are 57 signals that Google looks at -- everything from what kind of computer you're on to what kind of browser you're using to where you're located -- that it uses to personally tailor your query results.
He says they are signals used during ranking, not something to identify people.