Quite a coup for HP. Andreesen–who co-authored Mosaic, the browser that popularized the World Wide Web–is an icon in Silicon Valley and his expertise is highly sought. In addition to helming his new venture capital firm, Andreessen-Horowitz, Andreesen also serves as chairman of social networking outfit Ning and sits on the boards of eBay (EBAY) and Facebook. HP (HPQ) is lucky to get him, if only because it seems unfathomable that he’d have the time or bandwidth for anything else.

“Marc Andreessen is a software pioneer whose leadership has helped shape the Internet,” an ebullient HP CEO Mark Hurd said in a statement. “Marc’s entrepreneurial background and industry expertise will be a welcome addition to the HP board of directors.”

OpenSocial, as Google has named it, is a set of common APIs (application programming interfaces) that will enable developers to write applications for a broad range of Web sites and services without any individual customization. Think of it as Facebook CEO Mark Zuckerberg’s “social graph” but writ large.

And while some might smirk at OpenSocial’s initial roster of participants–LinkedIn, hi5, Ning, Friendster, Plaxo and Google’s own “big in Brazil” social network Orkut–it does include a few big names: business software makers Salesforce.com and Oracle. Oh, and Google. Which, as TechCrunch’s Erick Schonfeld points out, already has much of the critical mass it needs to push this effort forward: “Google already has so much data on you, depending on how many Google apps you already use. It just needs to bring everything together. … Over time, Google will connect all of these together in different ways, along with data about you from other social services across the Web, and give developers access to the social layer tying all of these apps together underneath. The real killer app for Google is not to turn Orkut into a Facebook clone. It is to turn every Google app into a social application without you even noticing that you’ve joined yet another social network.”