Hey,
OpenSocial finally launched in India a couple of days ago. Though a delayed release, there were some applications that did show up. I wanted to start writing applications too, but call it my laziness lack of time, distance from the 'hot zone', I had to settle with working on breaking these applications.
In my humble opinion, OpenSocial seems to have only increased the attack surface on the already flaky orkut. There were script injections when the flash was introduced in scraps, but the introduction of something as huge as opensocial is bound to open up a lot more vulnerabilities.
The first signs of problems that I noticed was with the emote application. This is an easy target for the script injection and I presume that taking control of one application could potentially be a starting point for more interesting things. Surprisingly though, even after firebug shows me the script that is inserted it does not execute.
Also, it may be a little difficult to reverse engineer the applications that have code inside the XML file using firebug breakpoints. This is because of the ifr?URL loaded every time is dynamic and hence, breakpoints will have to be set as soon as the file is loaded. To achieve this, an extension like Tamper Data could be used to wait till the script is loaded, and then place a break point.
Right now, I am looking at how to use emote to break into anything interesting, so watch this space for updates.