I have been on LJ for years before joining Facebook, and my friending was haphazard rather than systematic. By and large, I have successfully distinguished LJ users through the content of their blogs. In both places, the key is to detect how rewarding each site is to me when I use different friending criteria. I de-friend people if I find I am consistenly uninterested in their blog posts, with little regard for whether I know who they are or not. In some cases, if they don't post, I simply forget that I friended them.

For me, Facebook provides no interesting content at all. Rather for me it is good as a directory of people. When I meet someone at a party, and they seem to have come with person X, I look through person X's Facebook friends list to see if they have a directory listing so I can learn more about that person. Also Facebook is good for party invites and other alerts. So I need to keep it very tightly connected between profile and true identity.