[romaniv]

Part of what I mean is that Facebook design implies that you need to friend someone to interact with them on a persistent basis. And neither me, nor anyone I know would "friend" a person just because they've had some interaction with that person on Facebook itself. Even the wording (e.g. "friends") suggests some kind of offline connection.

Sure, there are people who operate differently, but I really don't see any evidence that FB is designed for that kinds of use. If you "friend" people indiscriminately, your list will mean less and less with each person added.

Another part is covered by reply of dfxm12.