Cygnus, over at SEOChat, posted a thread back in July that has quickly become one of the most popular and visited threads of the summer. Delisted Sites? poses questions about many recently dropped sites at Google from a variety of sources. I was lucky enough to have some private conversations with Cygnus to take a look at some of the sites, and while I'm not free to share them, I can say with some degree of certainty that there is great evidence to support the idea that if you link to "bad sites" and "bad neighborhoods", you could very well face your site being de-listed.

From my experience looking at the sites, there can be little doubt that the ban has been triggered by a scan of the website linking into and out of the site and the quality of the sites and links on both sides. I would urge SEOs, especially those in particularly commerical or competitive spaces to be very wary of how they build links on their sites and where they generate the sources of their links. Low quality coming in and going out appears to be something that can earn a quick reprimand form Google (despite being relatively safer at Yahoo! & MSN) and my recommendation, therefore, is to first earn links naturally, with content - use press releases, directory listings, blogs (not comment spam, but blog mentions in the posts) and creativity before turning to automated systems or link advertising.

This is one of the first major upgrades I've seen in Google's ability to punish low quality links and sites (and high quality sites with low quality links). It could very well be that further crackdowns are around the corner.