Key differentiator between this and Facebook platform is that it is Open standard, and developer are supposed to learn it once and apply their knowledge to write applications for all participating web sites.  Many of big social networking companies except Facebook have already announced that they are participating in this initiative and have parternered with developer to start building widgets for their sites.

Google OpenSocial site is live here  and official blog is here

Here is the list of big names who are already participating, either as host or developer for this platform;

MySpace, LinkedIn, Hi5, Ning,  Salesforce.com, Flixter,  RockYou, VistualTourist, Friendster, iLike,

All major tech blogs are following the story very closely.

You can read more about this at  TechCrunch, Gigaom, or at FaceReviews. 

I will be covering more about this platform in coming weeks and months.  I will be sharing reviews about different applications as well as tips, tricks, and articles about developing for this platform.