I'm gonna play Devil's Advocate (great movie!) about the Off-Topic Forum idea.
For one thing, bandwidth issues are already a very big thing here at ENWorld. Recent steps have made the boards run a little more smoothly, but the reality is that as the site grows in popularity (do we have numbers?) we're going to keep banging up against this wall. An off-topic forum, while interesting, might make this happen faster, since I imagine that would be one of the most popularly used forums.
Another problem I have with it is that at least one site already exists, started specifcally, AFAIK, because people wanted to post off topic stuff. That would be Nutkinland. There's no need to have it here if places already exist where off-topic posting can occur.
A third problem is that of moderation. IME, you have a lot more cases where moderation is needed with an off-topic forum. A lot of this would be because of politics and religion, which many people will assume they should be able to post about, and it's their right to post on whatever they choose. I'd like to think that ENWorld is different, but realistically the popularity of Nutkinland suggests otherwise (assuming my second point is indeed correct).
Finally, and it has been said, if you don't like posts, don't read them. I will concur, at times I've found it annoying as well, but unfortunately there's no filtering system set in place (that I know of) that allows a user to automagically weed OT threads so they don't show up. I would imagine it would use a fair bit of bandwidth anyway, since I see parallels to the search function.
