4.0 came out over a week ago, doesn't look like there's any major problems, and I just tested exporting this site and importing it into an MT4 setup - looks ok, so I might do the upgrade tonight while I'm working late.
With any luck, my next post will come from the new platform - and maybe my RSS exports won't get all screwed up and cause all my old posts to become new again, like I've seen in the past...