A few weeks ago Google launched a new feature intended to provide users with whois data in Google's main SERPs. By entering a query like "whois google.com" users are returned new whois data including creation and expiration dates in Google's main results. In addition to the new feature, Google provides users the option for more information via "Whois record for google.com" link which resolves to domaintools.com. After linking directly from Google's main search results to domaintools.com, users are greeted with various details about the domain including website title, description and even an "SEO Score" provided by domaintoools.com.
After linking from Google's main SERP to domaintools.com you might notice, there are lots of ads provided by Google. If you look closely, right along side those Google ads you'll find paid links passing PageRank at domaintools.com. Paid links passing PageRank are a violation of Google's Webmaster Guidelines and grounds for being banned from Google. In this case Google is linking to pages with paid links passing PageRank!
Here is an example using the cached text version of the domaintools.com landing page linked to by Google for the query "whois google.com" http://188.8.131.52/search?.... In it you'll notice http://vpslink.com... is a paid link passing PageRank. As I mentioned at SearchEngineWatch.com the paid link domain ranks #1 for the keyword term used in it's ALT anchor text at domaintools.com and linked to by the Google Whois feature.
If you would like more information about paid ads at domaintools.com and have $10k per month, click on the "Sponsor us" link to the right of the Google search box. I've not seen many banner ad landing pages with a PR of 6!
UPDATE: - In response to this post being picked up by blogoscoped.com, Matt Cutts (Head of Google Web Spam Team) confirmed earlier today that DomainTools.com is now in compliance with Google's Webmaster Guidelines. DomainTools is now blocking ads with paid links passing PageRank via robots.txt. Sincere and special thanks to Matt, Google and DomainTools.com for swiftly resolving this issue!