With the rise of Facebook and the arrival of the OpenSocial ecosystem, web site operators are left wondering about prioritization. Which social network(s) should I embrace, where should I invest my time, what site(s) offer the biggest bang for the buck if I build an application?

The folks at Compete have analyzed member overlap at various social networks and explain their findings in this blog post. The graph below shows those interactions.

Here are some of the highlights:

• 20% of MySpace members are also Facebook members.
• 64% of Facebook members are also on MySpace.
• Bebo, Hi5 and Friendster all share more than 49% of their members with MySpace.
• LinkedIn shares 42% of its members with Facebook and 32% with MySpace.

What it means: From a sheer size point of view, Facebook and MySpace are interesting but operators should not underestimate the reach of Bebo, Friendster, Hi5 and LinkedIn. Some of these social networks are very strong in different parts of the globe and, depending where your user base is located, could make interesting platforms for your applications. In addition, LinkedIn and Viadeo reach a business-oriented user base.