Postgres 9.2 gives you the ability to index and query JSON, but you still can't atomically update portions of the JSON which is very limiting.
It seems 9.2 can solve a lot of use cases but when they have partial updates, I'll cry tears of joy.
It's a common technique to serialize arbitrary data into blob fields in SQL databases--I've seen it for years. Usually, it is considered an anti-pattern. Postgres 9.1 doesn't do much other than verify the JSON data is valid JSON and then stores it unchanged, though successive versions are adding more first-class JSON support.