I've been on discussion boards with journal functions and they never interested me. In my mind, you decide "do I want to share things with people to get their response?" or "Do I want to record my thoughts and experiences privately?" I can't see doing a hybrid at all. When I have thoughts I want to work out in a journal, I don't want any voyeurs.
Just as an aside, the one time being able to access old discussion board posts turned out to be very helpful to me was when my computer wiped out a year and a half of my online private journal entries. I was devastated because there were significant events I had written about in that time period--the move to Vermont, the loss of my dog, etc. So, I went back and copied and pasted a bunch of my posts from this forum and others into my private online journal so that at least SOME information is captured.
But I will NEVER do the reverse and subject you guys to my journal entries!