I can't comment on the other sites you mentioned, but at EveryBlock, we've heard very positive things from publishers regarding the traffic we send to them. One local news outlet (not a blog) gets 20% of its traffic via referrers from EveryBlock. (I'm not sure whether that says more about EveryBlock or about that site, but still.) For at least three sites I can think of off the top of my head, we're the #1 referer -- i.e., we send them more people than any other site does.

Adrian