If you ask one of the people on Twitter “Why are you using Twitter?” I think the proper answer would be “to interact and establish relationships with other people” whether its personal or for business, but when someone answer your question by saying “I just follow the people that I know and the people that I’ve met personally before” then you should probably shout at them and say “Go and use Facebook, thats why its there!”.
I use Facebook to contact with my friends overseas and share pictures and stuff, but I’ve never used Facebook to meet new people because I thought its just too creepy for me, or it is a little dangerous to have a lot of information exposed to a total stranger.