I think it's a neat idea. Technically easy, but some of the best ideas are. I'm not using OhLife, but I coded a version (mainly to see if Google apps could be used to make a webapp, but also because people were concerned about privacy - the script's in the above thread); and I've been using it for the past week or so. I keep a paper journal anyway, so it's not really necessary for me on that score.
I'm mostly interested in the effect of their idea of being reminded of a previous entry. I think a week isn't long enough to tell; but so far a positive is that it shows I've made progress. It's reminded me of things I wanted to do (or problems I wanted to solve), that I have now done (or solved). So I'm using it partly as a technical journal.