Somewhat, but it's pretty limited in that it only verifies that the contents are valid JSON. You can't query against it with the built-in tools.

In a way, it's symbolic: it's saying that postgres is treating JSON and the developers that use it as first-class citizens.

Regardless, it will quickly and steadily improve.

It also provides a stable, preassigned OID. Because extensions don't really handle dependencies yet, this is critical -- making the extension "foo" that depends on the extension "json" is still rather far away.

That means projects like plv8 can more easily handle type conversions and so on. I think this is the largest single gain, and I think it rather considerable.

You can write simple perl/python plugins to create JSONPath index functions against JSON content.