Tim O’Reilly has put his finger on it…

If all OpenSocial does is allow developers to port their applications more easily from one social network to another, that’s a big win for the developer, as they get to shop their application to users of every participating social network. But it provides little incremental value to the user, the real target. We don’t want to have the same application on multiple social networks. We want applications that can use data from multiple social networks.

And data mobility is a key to that. Syndication and mashups have been key elements of Web 2.0 — the ability to take data from one place, and re-use it in another. Heck, even Google’s core business depends on that ability — they take data from every site on the web (except those that ask them not to via robots.txt) and give it new utility by aggregating, indexing, and ranking it.

Imagine what would have happened to Google maps if instead of supporting mashups, they had built a framework that allowed developers to create mapping applications across Microsoft, Yahoo! and Google as a way of competing with MapQuest. Boring! That’s the equivalent of what they’ve announced here.

Would OpenSocial let developers build a personal CRM system, a console where I could manage my social network, exporting friends lists to various social networks? No. Would OpenSocial let developers build a social search application like the one that Mark Cuban was looking for? No.

Set the data free! Allow social data mashups. That’s what will be the trump card in building the winning social networking platform….