Without the activity stream, following someone seems pointless :(
The other question would be why have the menu entry if it leads to no sensible result? I do miss the activity stream as well, and it telling me that I'm alone and to add more friends when I am following quite a few people seems pointless to me.
Have a lingot or two :)
I was following someone because I really like the answers and explanations he would give to questions about his native language, but it just doesn't work the way that it did now.
No, they should still show up on your leaderboard if you follow them.
But you can't talk to them, just see the xp count.