lzr0 - 8:32 pm on Oct 21, 2012 (gmt 0)
I would take it a step farther and suggest you find all common traits about your sites.
- Same server?
- Same Whois account owner?
- Same Webmaster Tools account?
- Same backend technology? (like wordpress or other CMS)
- Same Adsense or other ad network?
- Same look and feel or theme?
- Same niche market?
- Same type of site (articles, blogs, buying guides, ecommerce, etc) ...
I am sure it is more complex than that. After 09/29 3 out of my 4 sites disappeared from top search results where they used to be. These 4 are on two different webhosts, although they all have the same AdSense and Webmaster Tools accounts. Furthermore, both subdomains of one of the "penalized" sites were not affected and still rank high. Which seems to suggest that each domain or subdomain is treated separately (and common authorship does not matter).