Wow, what a great enhancement! Well done Bobster!
I may be incorrect here, but I suspect that it may affect the SEO ability of the site because if I use FF and disable javascript, the tabs don't work so I can't access most of the forums. Not sure if spiders would still be able to get around (as I assume the forums are just 'hidden' and the links are still in the source), but just to be safe, I would want a system that would show all forums if javascript was disabled.
Anyhoo, hope I wasn't talking out if turn. I think I am going to go have a gander at the mod bob as I think I could make use of it