• Co-Citation may be a similarity measurement used to establish subject similarities between two or more websites - maybe.
• If Y and Z are both cited by X, they could be said to be related to one another, even though they don't directly link to each other.
• If Y and Z are both cited by many other websites, they have a stronger relationship.
• The more websites they are cited by, the stronger their relationship is.
• In short, you don't want unrelated Casino and Viagra sites linking to you if you're not in those industries.
• Consider - SEO Heat Theory
  

Google Sandbox

• The Google Sandbox is highly debated
• Does the Google sandbox exist? Who knows - a 'Sandbox Effect' certainly exists
• For sure, new sites don't rank well in the beginning, especially if they have been optimised and don't have any quality sites linking to it
• I've seen 'effects', but do think it is about the niche, onsite optimisation, specific key terms and it could be anything from PR itinerating to a complete lack of trust or online business authority
• Got a new site? Get some links from real sites - quick.
• Consider - New sites take time to rank