I don't post anything in my LJ that I wouldn't be comfortable seeing on the front page of a major metropolitan daily newspaper.

Even though I use friends filters, it only takes one person to take a screengrab, and repost, and then my private thoughts can be spread across the internet.

So, I tend to be pretty private in what I post.

I also have to approve comments from non-friends, and have disabled (I think) anonymous comments.

It's very hard to have total privacy on the internet.