How many largish bloggers are there? 10,000 maybe? Certainly, when the pagerank hits a certain point, keeping a human-verified whitelist of sites is doable.
That is, if something is getting a high enough position on google, a google rep could look for a phone number and verify that a human, not a bot, is behind the content.
Of course, this will hurt short-term ad revenue...
You forget something: people that download said killsplog feature are not going to be running into splogs often (i don't). Other than that, I think its just fine...good for the economy. Eventually (as Eric S. ) said, advertisers will wise up, and start paying less. If they don't, good for google.
That is, if something is getting a high enough position on google, a google rep could look for a phone number and verify that a human, not a bot, is behind the content.
Of course, this will hurt short-term ad revenue...