I have close to 5000 friends in my facebook account. Facebook does not allow me to add more friends. I guess they have design issues related to this.
Let me give you and example. If I want to do something (say tagging a photo) which requires a list of names, it is so slow. It tries to download the list of all friends that I have (including their icons / avatars). I could imagine what 5000 friends will do. This is even worse with slow internet connection like what I have (and perhaps what other people have in developing regions).
Imagine if I have 10.000 friends :) and this is possible. I've been ignoring friend requests because I just couldn't add more friends. Currently there are more than 500 requests waiting. Almost all of them are legitimate requests. And why I get all these friend requests? Well, I hate to admit it but I do quite a bit of talk (to univesities' students, etc.) and in each talk there are more than 100 people. If 10% of them want to be friends with me, than 10.000 friends is within reach.
And I'll have more (scalability) problems ...
Clearly there should be a better way to do this. I don't know whether somebody in Facebook is looking at this.