I got some in my eye and it felt like needles jabbing me.
Remember that most perps are out to get something from you. That is, they have a specific goal such as getting your wallet or raping you or whatever. The people the cops end up spraying are usually just being violent a-holes and swinging at anyone. A cop is trying to apprehend someone, whereas you are simply trying to leave.
From what I've seen on youtube, pepper spray is effective at stopping people from setting and achieving discrete goals like firing a weapon or taking a purse or whatever. It's not so effective at preventing people from flailing around and causing havoc to those people and things nearby.
So if you're afraid of being robbed or carjacked, it might be good (provided the perp doesn't have a weapon). If you're afraid of being punched and kicked in an elevator, not so good.