I'm not sure if this belongs here, but its pretty interesting...
From http://www.seoconsult.com/seoblog/pay-day-loan-rankings-the-shady-tale-o...
Drupal allows the posting of comments on articles posted. These comments allow some basic HTML by default, including hyperlinks. These hyperlinks are the cause of almost every result in Google’s top 20 results for the keyword “pay day loans”. The hyperlinks do not contain a nofollow attribute which means that a spammer may post as many links in these comments to the pay day site as they want, and Google will treat them as ranking links.
I know that everyone in this group probably enables antispam countermeasures on their sites (right?!) such as mollom, captchas, nofollows, etc.
That all being said, this author is correct when he states
Personally I find it amazing that Drupal does not include the nofollow attribute by default.
I tried to find a core issue request, but was unable to. Does one exist? I can't imagine that it doesn't :)
F'n spam...