Using jsonb also brings the headache of having to worry about the version of Postgres you're using. Simple functionality like updating an object property in place might be missing in your version. And the documentation and stack-overflow-ability of json/jsonb is not very good yet.
But as an alternative to things like serialized objects, I think it's definitely a huge win. You can do things like join a jsonb object property to its parent table, which wouldn't be possible with serialized objects.
And why is this a headache? Every time a new feature is introduced, you have to worry about the PostgreSQL version.
If you're developing an application in-house, this is not a big deal - you can make sure you have the right PostgreSQL version. If you're hosting the application on a shared database server, well, you're exactly in the same situation as with other software products.
But as an alternative to things like serialized objects, I think it's definitely a huge win. You can do things like join a jsonb object property to its parent table, which wouldn't be possible with serialized objects.