If you open a thread that you don't want view, just hit the escape key to kill the pictures loading then the "back" button on your browser. Or just hit the "back" button. How lazy can you be?
Having administered forum and bulletin boards in the past, as well as working with databases for a living it is always easier to start out with too many categories than to split them later when there is a large number of posts or records. Sure, Andrew can create new categories and say "from now on posts about x go in the x forum" but that violates my sense of data integrity because of all the previous posts on x are now mis-categorized.
As JC pointed out people should just tag properly their topics to begin with which would make it a lot easier to filter out what you don't want to read. That's why these features are there.