In the last two years I've been using JSON in almost every project I was involved in.
For example with APEX Office Print our plugin is sending JSON to the backend. This JSON you can actually see yourself in the Remote Debug screen in your AOP Dashboard.
Another example is the wearables project (IoT) I showed at KScope 16; the wearable is sending data to a smartphone or tablet, which in his turn is doing a call to our backend (in ORDS) and sending JSON across.
At the end of the day we want the data in the Oracle Database, so our APEX apps can work with that data.
Since Oracle DB 12c, JSON is supported straight from the database. I wrote a number of blog posts how to read JSON from SQL within the database. Here's a quick demo of JSON in the database:
Edit 4-AUG: return null is default behaviour of Oracle, but you can specify you want an error instead. See the comments of Alex and Beda.
Edit 4-AUG: read the comments section for a way to get the CLOB out with PL/JSON.