I might be able to make a change such that each thread has a category, but the icons aren't displayed on the main forum view. That might appease the "they're ugly" crowd whilst still allowing others to filter if they so desire.
Belatedly, I've sort of implemented the above. At the top of the Big Board there is a new filter which will help you select any particular flavour of thread you only wish to see.
The results are limited at the moment, obviously, as the thread categories are new.
I welcome all feedback and...