I do make f-locked posts from time to time, but I don't use LJ as a private journalling tool. In this case, I wrote up a post which pointed at several specific people in a way which would not reasonably remain anonymous. Not to deride or insult, but simply by reference. I decided that it's not fair of me to "out" people, and if I'm going to name names, to just do that. Politeness, and a desire to respect other people's social privacy and personal boundaries, are both pretty important to me.
My basic rule here is that if you make public statements in the blogosphere or in print, I can cite you or respond to you. If you make statements in the comments section of my LJ, unless you've specifically requested privacy/anonymity I'll quote you at whatever length might please me. Not that it comes up very often, and I always strive to be respectful.
snippy was talking recently on her LJ about this issue of boundaries and social responsibility in online discourse. It's interesting to me. I'm not sure where the limits are. Right now I'm going with the Potter Stewart test — I'll know them when I see them.