Building up a contact list to feel like you have friends.. but do you?

This is yet again one of those things drifting in the back of my mind.. and it just surfaced into a proper "meaningful" theory.. i hope
Have you realised how people have sooo many contacts on msn? or icq? or any other IM?
Have you also wondered how many of those 1xx contacts do you actually talk to?
I've realised that those who you talk to often in real life you tend to talk to more often on IMs..
Those who from the start you don't talk at all will end up being on your list just to make you feel special.. sigh
On another note, I've realised that those I talk to in real life may not read my blog.. yet those i don't know as well read it often.. how interesting..
What then determines their degree of friendship? :P i dont want to be measuring etc.. but i get confused..
do people have to know me both "inside and out" to really be a good friend?
Ive heard once on MYC that those who come to your house at least once and go somewhere other than work/uni related will be more likely to stay friends with you longer.. i wonder.. is that true?