http://news.bbc.co.uk/1/hi/technology/7539329.stm
"For the purposes of the study, two people were considered to be acquaintances if they had sent one another an instant message."
I wonder if a distinction is made between two friends who communicate frequently, and the case of "Hello, I'm an IM spammer" and a response of "Go away you idiot" (or words to the effect).
Because that would effectively join a lot of networks to be a lot closer than they really are, simply because the spammers contact so many people with value-free communication.