Remember the "ghost" in Ivarstead (I think it's Ivarstead) that everyone's so afraid of? Then you go into the dungeoun and fint out he's a man with a potion. Well, everyone but you are totally scared of this guy. So you kill him. Then you can loot his pots and drink them, turning YOU into the "ghost".
You can go back into town while being etheral and no-one will remark on it. IMHO this is a poor design choice, I mean couldn't there at least be a reaction when you are disguised as the ghost? What's the point of getting the potions if the effect is 100% visual?