In my recent review of Day One, I listed a few ways to put the journaling app to good use. Over at The Sweet Setup, Shawn Blanc's review of the same app contains a running list of other great ideas worth checking out.
This bit at the end is so true:
“Thanks to tagging and searching, Day One can serve as all of these things at once. That’s the beauty of a personal journaling app, it can be filled with all sorts of topics and media types, with no need to keep it “focused.” And I think that’s the road best traveled. Because a huge part of what makes a successful journal is constant use.”