Ok, here's my first post using the MT4 interface.. Upgrade seems to have gone mostly fine.. except where did my categories go? I hope I didn't lose them..
Nevermind, the interface just looks different.. Ah, progress.
Update: beware the templating changes.. apparently MT4 templates are way different from MT3 ones, and blindly picking a new MT4 style in the style chooser will lead to very weird results. Here's a post about how you might actually go about upgrading your template.