dibbern2 - 5:19 pm on Apr 22, 2011 (gmt 0)
I hope this isn't off topic, but I think it is a sign of user engagement/user behavior:
If you search a topic, click on a serp and follow it to the page listed, and then hit BACK to return to the G serps page, this message appears under the listing you had previously clicked: "Block all results from sample.com"
Is this possibly a "NO" vote that will go into the site's profile? G is assuming, I believe, that since we followed a link and bailed back, there is something we don't like about that whole domain.
I leave it to the smarter heads here to comment.