Dare Obasanjo has written what is probably the most detailed critique of OpenSocial that I have seen so far. Most of his post enumerates the things that are still missing from the documentation, such as the Activities Data API, the Service Provider Interface (SPI), or any details of how the user can control the applications access to personal data. He also brings up some more substantive points:
- No user interface hooks, even for common operations such as interacting with a Friends list
- The data in represented as Atom feeds, which can be very convoluted.
- The persistence data API only supports key-value pairs.
- The spec is not "open" in the sense that it is owned by a standards body instead of Google.
- There is no mechanism to map identities among different container sites.
Of course this last point does create an opportunity for application developers.
We all await developments on the Google OpenSocial blog.
Also, see Niall Kennedy's survey of widget formats.