A suggestion: I liked the ability to move to top of page from any post, saved scrolling for me. I see you have a go up / go down at bottom and top of pages, helpful, but to do at least go to top from any post would be better, at least IMO.
Don't know if that works on all browser but with FF ctrl-home (top of page) or ctrl-end (bottom of page) should do the trick (and avoid to have too many nav links cluttering the space around messages).
After the first puzzling moment of "what's where", I'm amazed that such a major change did go with so few glitches.
I didn't see any, connecting now... apart from the things that google still links old post adresses, which are not compatible with the new board giving only 404 - is there a way to make a redirect?
Google may re-index the forum, but there are a fair bunch of links here and there, eg in other forums (so that people may know what is a good one like).
For the GUI side of things, I'd like too some more delimitation (a frame would be good, or a black title box as in the "topic summary" presentation I see right now in the post reply page)*.
To look at good things, I particularly like the way photo thumbnails expand in the page on clicking, rather that opening a new window/tab.
Edit 1 : Another little suggestion : in another SMF forum, I can hover on the title of a post in post listings to see the beginning of the message - very practical to decypher a not-so-well-chosen post title. Could this be implemented here, please?
*Edit 2 : the windowbg2 css object might control the frame, and there might be a postsep object too between posts?
Just some quick'n'dirty guess based on css inspection and another SMF site, so this should be taken with a truckload of salt but I wish it might help.