As many of you probably know, my first MMO was Final Fantasy XI, which made adding someone to your friend list a sacred procedure in which you sent an invitation for mutual friendship and prayed that it was accepted. I believe at some point it was customary to offer a small gift, perhaps a fatted calf. The point was that it was a very specific procedure, and I got used to the idea that a friend list was a special bond in which you only added people you really did consider friends.
This is not a view held universally. Heck, this was not a view held universally in that game. In games with more casual friend features like Star Wars: The Old Republic I would find people putting me on their friend lists after one or two interactions that were fairly positive. There was a disconnect from my practices, in other words.
Of course, I also know there are other people out there who only fill friend lists with specific sets of people. So how quickly do you friend people in an MMO? Do you do so after just a few interactions? Right away so you don’t lose track of them? Only after an extended interaction and, yes, the exchange of valued livestock?