I updated my WordPress installation to the version 2.3.x and found a new feature: tags.
I converted all my categories to tags (except the Uncategorized category) and… what I saw a small disaster :) All categories disappeared (an expected result), but the categories list in my sidebar contained only one, not very useful, item Uncategorized. Additionally a blog entry contained only Filed under: Uncategorized, again, not very helpful.
And then I realised - I have my own theme… arrrrgh…. and there is no tags to categories converter ;>
Well, here are steps how to update your own theme to support basic tags features:
(There is more where this came from … )