If the Platform Rush of ’07 was about creating APIs for third party developers to build applications on social networks, the Platform Rush of ’08 is about extending those platforms to the rest of the open web.

Before May of 2007, it was impossible for third parties to build anything on Facebook. At the same time, MySpace was kicking third parties off the site left and right, disabling off-site clicks in Flash widgets, and generally wanting to own the entire experience itself.

My, how things have changed quickly. On Thursday, MySpace announced a Data Availability initiative that will allow users to share profile data and friend lists via their REST API with OAuth authentication. In a curiously timed Friday afternoon release, Facebook announced its Facebook Connect initiative which will allow third party websites to access Facebook users’ profile data and friend lists (consistent with users’ Facebook privacy settings) via new Facebook Platform APIs and authentication. And on Monday, Google is rumored to be announcing an OpenSocial initiative called Friend Connect, which will do much of the same thing (though perhaps with more restrictions).

Social networks have had so much success “platformizing” themselves over the last year that they are now rushing to embed themselves into a new “social” layer that sits beneath the rest of the Internet. The hope is that where a person’s profile is, there his trust will be also. By enabling users to share their profile data, friend lists, and privacy settings with applications all over the web – not just with applications on Facebook.com or MySpace.com – social networks will enable new classes of web applications that take advantage of the deeper social context never before available to almost everyone else. And thereby, in the process, make themselves an increasingly important part of the Internet’s infrastructure.

Why? Infrastructure plays usually have different business models than $.10 CPMs.