I'll add SO of friends or sometimes people who post in friend's journals. E.G. I read a comment in a friend's journal posted by a friend-prime, go check out the friend-prime and decide they are / might be someone I want to read, so I add them. I've also done the same thing when browsing communities even when I didn't add the community or dropped the community later.
I commented in another friend-prime's journal that I think LJ has returned us in a sense to an earlier time when there is more emphasis on writing and talking to people through writing.
Still I agree there are some squicky things going on.