Ha----I only have like 10 friends on XBL and most of them I don't even play anything with. In fact, besides a month long spurt of Modern Warfare 2, I don't play with friends a whole lot in general. I DO play online all the time, but not usually with people in my friends list. But I can see the younger crowd having a friends list of more than 100 because their lives revolve around "friending" people.
PS--Oddly enough, I play more multi player on PSN these days than XBL. All my friends at work have NFS Shift and MAG, so we play those just about every night.