I don’t think this will go the lively way, but it will surely be demoted later. Google always had the “Dissatisfied? Help us improve” link at the bottom (Yahoo doesn’t, btw), so we might see this “feature” going half way between the two.

(Continue of the short discussion on my blog)

They use their logs all the time, but here, for the first time, they get access to data the a user specifically doesn’t want a certain website (instead of just ignoring it in search results). In fact, Expert Exchange (which we already discussed at your blog) shows up first in my search results, I click it, so Google’s logs must think I really like the site.

True, I almost always click on other results as well because I don’t really get my answer – but sometimes I don’t, and this is where the explicit NO vote comes in handy.

You’re right that it dirties the interface, especially for novice users.

P.S.
You really should install some comment preview/editing plugin.

Google have enough knowledge from their huge search logs to filter ExpertExchange and I don’t know if you have noticed but you don’t see them that often lately…

How helpful the comments will be is a different question – I agree with you that it’s dubious they will do more good than bad.