It's not going to be long before we need to move to a whitelist model, rather than a blacklist model.

It ironically makes me think of the Yahoo Web Directory in the 90s.

Time is a flat circle.

This. I think, well curated web directories (by humans and machines) deserve a comeback.

Yes and no.

Power-law relations mean that a small number of domains will account for the lion's share of low-relevance results, and filtering those out will result in dramatic improvements in relevance.

That small set is probably fairly dynamic, however, and will likely change at a fairly high rate over time.

Penny-ante sites are less likely to appear in generic results, but might well be whatever the spam/phish term is for junk general Web search results.

We may well come to rely more on whitelisting, but I think at least for now that's not necessary, largely due to the dynamics of publishing / attention economies themselves.