OStatus is a social networking protocol standard in form of RESTful interserver HTTP exchanges.
It was designed by the Identica folks with a Twitter kind of use case, therefore it is still very limited on the privacy side.
We don't use OStatus since we're not so convinced of the traditional federation architecture, that OStatus requires, anymore.
Also because PSYC's social extensions are more efficient.
We do however share some concepts like activity streams, although we haven't actually implemented them into any client yet.