I've dealt with the same concerns over the years, but over time I've relaxed the separation a bit. The only time I've been "discovered" is when a particularly determined childhood friend tracked down my LJ username via a TinyMUSH mailing list message that was in a public archive... and I was glad to reconnect with him!

At this point I don't want my family reading my journal (husband excepted, he has full access to my brain) but anyone else is welcome; I just try to keep the sensitive stuff access-locked.