And by this, I don't mean remove the forum topic/reply posting system, I mean remove the automagical Forum_Id association that lots of forum systems use. In Database terms, forums often consist of posts which are assigned to topics, which are assigned to forums, which are assigned to categories, which are assigned to boards. I'm thinking that in the times of wikism these forms of categorisation are out-dated.
Take, for example, the "Your Announcements" and "Help Wanted" forums. Imagine if the poster was both pushing out an advert for thier project but also wanting someone on board to help out - which forum do they post in? What about someone wanting to use a new HDR algorithm in OpenGL, do they post it in the OpenGL forum or the GFX Forum? Database questions - General Programming or Web Development - it's clearly neither, but I've started seeing a lot more topics on both these days.
So what do I suggest? Categorisation systems that are user-defined by way of tags. Instead of forums, use the tags to create your own views of the topic pool (of course, a forum should supply a bunch of presets to help the lazy). "Show me all C#-based Database questions", "Show me all C++, OpenGL questions about HDR", etc.
I might have a go at making a proof of concept.