Howto write an application for social networks

I've been seeing more and more applications for social networks (like Hi5). What I didn't realise was that it existed a standard API for developing those applications. OpenSocial is a reference API by Google that is being used by some of the major social networks (LinkedIn, Hi5, MySpace). It makes sense as it allows a developer to create an application or gadget that works in several social networks, or even allows communication between those.
And this explains the amount of new applications that are emerging every day. Still, it amazes me how a consensus was reached to allow this to happen. I thought only W3C had the power to do that. On the other hand, Google is becoming more "standard" than anything else...
On the technical side, the OpenSocial site seems quite good, with lots of documentation and sample applications. I didn't have the time to read the API itself, but being so well documented it's a great thing. It makes me think it must be easy to implement this kind of applications. It makes me wanna implement something :)
This also makes me wonder how many interesting Google projects are there that I still never heard of...