>But the body text is even more important, and that goes at the bottom. So I dunno.
Yeah, I considered this too. I'm mainly suggesting for the sake of convention.
We definitely don't need a separate page for creating new threads (I get bad memories of Shiichan), mainly because it's inconvenient and requires a whole other page for something that really shouldn't. The fact that it'd be at the bottom of the board page already detracts bad posters with itchy trigger fingers. I think most of us have an "End" key on our keyboards, so we don't really have to scroll all the way down anyway. :) Really, the only issue I have with moving the post box to the bottom is that it ruins my personal visualization of new threads falling on top of the "stack of threads" and replies emerging from below the "stack of replies".
In reference to >>90, there's something I see on every 2ch board that is a lot less prevalent in Western counterparts (barring certain 4-ch boards): a rules/disclaimer block at the top, above the thread-list, with links to a newbie guide, site FAQ, and the like. Yes, it may be an annoyance to veterans, but being at the very top means it's most visible to newbies. That way, we don't get a constant influx of people wondering whether or not they need to fill in the Name and Link fields and what the hell sage and tripcodes are.