OpenSocial turned 1, what's in it for us?
It has been a year since OpenSocial came into the world of Social Applications and it's now adopted by several prominent social applications spearheaded by Orkut. You can view a compliance matrix of current OpenSocial containers if you are a Mashup Guru / Gadget Developer.
So what does OpenSocial add to one's toolbox? As its name suggests, the 'Social' features. For example, when you are developing your Social Application (a Gadget), it obviously needs to know about your users' friends and their publicly available details (ex: birthdays). If your Social/Mashup platform is an OpenSocial compatible container as well as a legacy gadget container, you can access this information from your social application. Not only that, but because you talk to your Social Platform through OpenSocial, now your application can talk to other platforms implementing OpenSocial without you having to change your code. As usual, this is the simplest explanation I can think of at the moment.
Untill I get more time to write on this, the following series of screencasts should be helpful if you are an application developer.