By choosing Pg over MySQL or Mongo, you are selecting a high-quality, stable product that is on a very slow and steady development trajectory with very few missteps along the way.
If you don't want to be surprised by the interesting and unexpected ways your database functions, choose Postgres.
Native JSON support is coming in 9.2 (being released very soon) and will rapidly improve.
PostgreSQL is being used by startups and major enterprises alike to great effect. If you have any interest in it, I encourage you to dive in to some real problems and see how postgres can help you solve them.
Yes, your criticisms may be valid, and postgres is always improving. But if you keep an open mind and actually try to solve real problems with it using all of the tools it has to offer, you may be pleasantly surprised.
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.
If your intention is store data structures in JSON form -- ie pretty much a pure graph database -- then maybe a relational database engine is a bad fit anyhow.
If you don't want to be surprised by the interesting and unexpected ways your database functions, choose Postgres.