Facebook has safeguards such as requiring a certain amount of friends in a certain network to add you before you actually become a part of that network (i.e. a high school network), and if you don't meet that quota in a certain amount of time they disconnect that account. Facebook also sets a limit on the number of friends you can add in an amount of time after you join their site, i think its about 100, more than that and you'd trigger flags and they shut you down and don't let you do stuff.