I've tried it twice and not liked the side effects. I tried it many years ago for Deska's seperation anxiety. And more recently with one of the cats.
Deska became way too over confident and a bit of an air head. So he'd just wander off on walks, he wouldn't listen and he'd sometimes just stand and stare at nothing (as far as I could see). I decided not to continue with it. The cat was very dopey and actually became fearful of me so I stopped it after 2 weeks. That said the 2 weeks was enough to stop the cat fights.
Nowadays when Deska gets over stressed (he a sensitive boy) I give him valium, he probably could do with something longer term but with his arthritis meds I'm kind of limited. I have seen quite a few dogs do well on fluoxetine though, and would probably have tried this with Mr D otherwise.