It's pretty simple – if you know the person, add them as a regular friend, if you don't know them, put them on a limited-view profile and add them as a mafia wars recruit. If you're not sure and don't want them to get angry because you added them to a limited profile, just ignore them, 99.9% of the time, if you don't know them well enough to actually know you know them, they won't even notice.

A simpler approach is to just add those people you actually know and those who have added "Mafia Wars" to their request lines – you should do that as a rule anyway. You might miss out on a few people who don't know protocol, but it's better than worrying about it.

Well if they're your real life friends, shouldn't you know them? =/ It's simple, really. Pick out which ones you know and which ones you don't.