It's such a fine line. Put too much detail into a spec and you gets accused of telling the programmers how to do their job. Put in too little and they deflate your wading pool.
Desmond: I have a question about your spec.
Desmond: It's about section seven.
Owen: Desmond, my spec documents every facet of this product exhaustively. You'll need to be more specific.
Desmond: It's blank.
Owen (leaving to go swimming): I left the details of the implementation up to you.