There are indications that Google is changing OCT 24 2007
There are indications that Google is changing their PageRank algorithm, possibly to penalize sites running paid links or too many cross-promotional links across blog networks. Affected sites include Engadget, Forbes, and Washington Post. Even Boing Boing, which I think had been at 9, is down to 7. You can check a site's PR here.
Depending on the site, 30-40% of a site's total traffic can come from search engines, much of that from Google. It will be interesting to see how much of an impact the PR drop will have on their traffic and revenue. (thx, my moon my mann)
Update: Just got the following from the editor of a site that got its PR bumped down. He says:
Two weeks ago I lost 80% of my search traffic due to, I believe, using ads from Text-Link-Ads, which does not permit the "nofollow" attribute on link ads. That meant an overall drop of more than 44% of my total traffic. It also meant a 65%-95% drop in Google AdSense earnings per day and a loss of PageRank from 7 to 6.
He has removed the text links from his site and is negotiating with Google for reinstatement but estimates a loss in revenue of $10,000 for the year due to this change. And this is for a relatively small site...the Engadget folks must be freaking out.