What LJ friends have you known longest?
I went to high school with ben_leviathan, though lost contact with him for some years afterward; I met strangehours and cyflea at university some 10-12 years ago, and have known some people from the net (notably mporter and kbuxton) for a similar length of time.
Is/are your significant other/s on LJ?
Not at the moment
Do you have LJ friends you've never met in real life?
A few; mostly people I know from when I hadn't met most of my friends, and whom I hadn't yet met; that and a few people I don't know personally but who use their LJs as fairly interesting blogs (such as jwz).
(I also use my LJ account to aggregate various interesting RSS feeds into my Friends page, for ease of reading.)
Do you have friends you met first on LJ, then in real life?
Most people who fit this criterion I met through means other than LJ, such as blogs, mailing lists or even USENET (which probably shows my age). Some have since gotten LiveJournals; others I'm still encouraging to do so.
Does it hurt your feelings when someone unfriends you?
No. Mind you, the only people who have unfriended me so far have been random strangers who, for some reason, thought my journal would be of interest to them; some of them have been creepier than others.
What would make you unfriend someone?
Not finding their journal interesting. If they're a stranger, then the threshold of what's interesting is set somewhat higher than if they're somebody I know personally. I'm generally not interested in the mundane details of people's everyday lives unless I know them, but I'm happy to read perfect strangers' blogs if they post interesting things.
In theory, anyway; in practice, I'm less likely to unfriend people and deny them access to friends-only posts if I have a connection with them. (Which, I think, is another argument for splitting the Friends list into separate "reading" and "trust"/"privilege"/"connection" lists; but I digress.)
Do you discuss personal information in your LJ?
My LiveJournal is pretty much exclusively for personal information; that and information that benefits from being friends-only, and experimentation with social software. Everything else goes in my blog.
Though if by "personal information" you mean "intimate details of your sex life/mood swings/medication dosages", then the answer would be no.