Very good point. Of course, a cron which regularly checks the stored function from the db against a copy in the version control system and updates the VCS (and possibly complains somewhere via email) if the db copy changes is pretty easy, but is also just another thing to go wrong.

Then again, you could argue that your db schema is as much a part of your app as such stored functions and the same applies to them. If you already have scripts to recreate your schema under version control (which some people do) then you could consider this as part of the same?

Sorry for continuing this theme ad nauseum, I'm just intrigued by the pros and cons of this.