Seeing as there are people on both sides of the fence, maybe you could make the new categories available for searching rather than making it the only way to view the site altogether. This would mean that as you entered the forum you would be given the choice of viewing 'categorically' or 'singularly'. Personally I would rarely use the different categories, as I like the way it is, but If I was trying to find a specific thread then it would be useful now and again.
Thanks for the site.

Ian