A New Kind of Journal

Someone just asked me how blogging compares to journaling, and I got really smarty-pantsy about it for a while before thinking, This would be a good question for a blog. So let me put it to you, my few and far between readers: In what ways is blogging like journaling, and in what ways is it not? What would you be sacrificing by journaling online rather than privately, and what are the positive side-effects of such a practice?