I like the idea of a wall, too. I had an idea last night, regarding this. When commenting on someone's wall, you could check a box to make that post private. Only the commenter and commentee could see that post, but it would appear in line with the rest of the posts, so as to preserve the timeline. These posts would have to be very obviously private, maybe with different colors or a big '''Private''' header or something. Users could have the option of only allowing private messages on their profiles.
