Friends only.
I'm pretty easy-going about adding people to my f-list, even if we're not acquainted, but I like knowing a thing or two about the person before hand--if we have common interests, if went to the same university/high school, are active in the same communities here on LJ, things like that. I don't like being inexplicably added to other people's f-lists, and until there's some communication between us, I won't return the favor.
That being said, do comment here if you'd like to be added. Comments will be screened.