This week’s release of the new Open Social web API supported by Google, Ning, LinkedIn, Friendser and others may be a milestone of sorts in the development of the web-as-application - what some are saying defines Web 3.0. Web luminary Marc Andreessen, who thought Facebook was a dramatic step, calls Open Social

“…the next big leap forward. Open Social takes the Facebook platform concept and provides an open standard approach that can be used by the entire web. Open Social is an open way for everyone to do what Facebook has done…including Facebook itself, potentially (Marc’s post continues here).

The San Jose Mercury reports reports that Open Social will let developers write one program that can be used on Ning (Marc Andreessen’s startup), Orkut, Friendster, Linked In, Plaxo or any other service that participates. Of course all this comes as Google, Microsoft and Facebook are squaring off in a battle for the social-networking advertising market. And, they report, not everyone is so sanguine about Open Social and have concerns about the privacy issues.

Regardless of labels (Web 2.0 or 3.0, take your pick) and the legitimate privacy concerns some have focused on, Open Social looks to me like a big step towards the the next generation of web services where users expect to be able to customize their experience, where social connections as well as data connections are the norm. Marc Andreesson has posted a series of screenshots and videos on his blog that show Open Social in action and you can Google Open Source API for more info.

>>> Update 11/4/07: Why Google Turned into a Social Butterfly in the NYTimes discusses Open Social in depth, compares it to Facebook’s ‘island’ approach, and observes,

“If Facebook chooses to remain a holdout, it will not be as the head of a counter-coalition but as a cranky recluse. [...] So far, every time the Web has matched up against a proprietary alternative, the Web has prevailed.”