All_source comes to the rescue, I'd say that it is a special view that holds all the database objects accessible by the user.
Here is the description on the view's columns:
| || || ||Owner of the object|
| || || ||Name of the object|
| || ||Type of object: |
| || || ||Line number of this line of source|
| || ||Text source of the stored object|
I need to find out who refers to column FK_USER.
select * from all_source where text like '%FK_USER%'
And I will get all the places which have reference to FK_USER.
If you would take it further, you could utilize it for searching almost anything (e.g. comments in the code, TODO tag, exception).
... wondering if there're more "magical" view like this.