I upgraded to wordpress 2.3, which has as its main new feature support for tags. So I installed it and got busy converting my wordpress categories to tags using the wizard and then updating the theme to display them as discussed here.
Currently all my old posts are rather poorly tagged. The intention is to not be restrained by fixed sets of categories and freely associate keywords with the posts. Things will get better over time as I add new content.
Other than the tag support there is not that much exciting new features as far as I can see.