Correct me if im wrong but im certain i also read that racial traits for barbarians include stun immunity.
Also, on the rescue bit, as frog said, best kept for emergency situations. I must admit on certain occasions for some unknown reason if i lose aggro on pull i do use it but that is because i know if i don't get it on me raid will wipe soon.
Yes it depends on the situation but for me its one of the last resorts. Mind you surprisingly i have managed to pull a raid named by just using impede

and that was very recently and yes i got a way with it.