Skype was supporting tens of millions of concurrent active users on a sharded PostgreSQL setup years ago (like, 2006-07 or so). Yes, the support wasn't native, and they had to write PgBouncer and PL/Proxy to enable that kind of scalability, but they Open Sourced both projects, and they're pretty widely used in many environments for exactly that purpose.
As far as JSON, the HStore extension has been available some time since 8.3, which was released in 2008. Again, not native (though that's being addressed with 9.2, which should drop any time now), but not particularly difficult to use. A trivial web search shows people using JSON with HStore at least as far back as 2010, if not earlier.
Skype added sharding support themselves. And it requires you to use stored procedures instead of SQL making it unusable for most users.
And I am talking about native JSON support as a first class citizen. Nobody is going to lock their entire data structure to a third party extension that may or may not disappear.
Skype was supporting tens of millions of concurrent active users on a sharded PostgreSQL setup years ago (like, 2006-07 or so). Yes, the support wasn't native, and they had to write PgBouncer and PL/Proxy to enable that kind of scalability, but they Open Sourced both projects, and they're pretty widely used in many environments for exactly that purpose.
As far as JSON, the HStore extension has been available some time since 8.3, which was released in 2008. Again, not native (though that's being addressed with 9.2, which should drop any time now), but not particularly difficult to use. A trivial web search shows people using JSON with HStore at least as far back as 2010, if not earlier.