I actually just put this on one of my sites (UBB.threads 6.2.3), and it works great!
Actually, there is one thing that isn't working. According to the instructions, if you make an image called "board.gif" and place it in the ubbthreads/images folder, it will appear on any forum that you do not have an image created for. Well, that doesn't work for me. It doesn't add any image to the ones without an image.
Otherwise, works great!