I've just downloaded the "Category Overload" plugin from Alex King's site to try it out. After installing it, the new WP2.5 interface prompted me that there was an update available.
I proceeded as normal, but the CategoryOverload plugin was replaced by a "404 Notifier" plugin, another one one of Alex's.
I think there's a link wrong somewhere. No matter - I'll try them both! But it should still work properly!