A topic most SEOs already know, but it is nice to have confirmation from Google. A
Google Groups thread has Googlers responding to a Webmaster who's site dropped from a PageRank 4 to a PageRank of 0. It appears this site saw a drop in PageRank, but not a drop in rankings, because it has done Paid Review posts without a disclaimer, said Google.
http://www.seroundtable.com/archives/015714.html