Well, if you're being personal, usually just because I'm bored, and I find other people to be possible catalysts for making entertaining things happen. I've never really felt any
need to be around anyone for any other reason, though. Occasionally, I do encounter one person that I find more interesting than others, and I find being around them enjoyable, but I'm perfectly capable of enjoying myself just as much without them.
I don't know if I'd really count MMOs and forums as socialization. In both cases, they can be like low-level puzzles. All you have to do is figure out what to type to get a positive outcome. It wouldn't matter if the person on the other end was actually a person, or just a computer.
A LAN party is actually socialization, though, albeit a more structured form than what you'd find normally. Everybody there has something in common, and everybody has a pretty good idea of what everybody is going to be doing. You still have to be able to get along and follow the cues of other people around you and not act too weird and freak everybody out, though. That's really what a large part of socializing is in the first place.
I was at a LAN party just last weekend, actually. Fragfest 16. Fun stuff.
