My immediate thoughts...

Having experience with Invision Power Boards, VBulliten, Proboards, and obviously UBB, I have to say...whoever designed this layout needs to be fired. It is way too cluttered. There needs to be an option to turn off the entire left column, at least outside of the main page.

I don't mind all the columns for the main page, but for the posts, the post(s) should take up the whole screen as it is currently, not 3/4 with a bunch of useless links and other crap on the left side that I don't need to see 24/7.

I like the idea of bigger avatars, attachments, quick replies (please add this, its really nice... ). However, the aesthetics are HORRIBLE. I mean, yes, the functionality will be spectacular, but this layout is absolutely terrible, it hurts my eyes.

I'd look into some sort of custom layout or skin, Geoff, to get rid of some of these things. Less is better, imho, and if we can get rid of all the columns and boxes outside of the main page, I'd be 100% in favor of this switch. I really think that the pros are great, and the cons, with the aforementioned exceptions, should make for a better forum. I have to think other people have had similar problems with the UBB upgrade, so maybe there is some sort of mod/skin/hack or customization feature or add-on to fix this train wreck of a forum layout.