I mainly keep my journal "Friends Only" to keep it out of the Google Cache and the eyes of my employer as I do occasionally rant about work. If I notice someone has friended me without a message first then I will read through their own LJ and decide on whether or not to return the favor. There are some who just add people so they have larger friends lists. A couple of years ago some local 15 year old girl friended me and I have never returned the favor as it kind of freaked me out.