Aside from the squished-in-the-middleness that's already been mentioned, I'm not finding the new forum to be too bad – it's good to be able to mark everything as read, as I either couldn't find that option on the old forum, or it wasn't there at all.
Also, I like that I can now upload an avatar, rather than having to join that Gravatar service in order to do so!
I did spot a couple of problems, during a quick catch-up of the topics I haven't read yet, though. Specifically, apostrophes in some posts (but not others, oddly) all have backslashes after them, and things using the quote tags, formatting tags, and some other tags from the old forum are broken and simply displayed as-is (that is to say, the tags are visible, and their effect isn't applied). Some posts are in a different font and have scrollbars within them, too. I also spotted a couple of posters who the forum has labelled as guests, whose posts are marked as needing moderator approval – is this a problem or is it just because guest-posting is enabled?
Also, even though the old posts seem to have the correct names, it looks like a lot of post-counts are wrong. I can understand if this isn't possible to fix, though.
Also, a quick question, if I may: Is there any way to see, at a glance, whether you've posted in a particular topic or not? I'm used to forum software that puts a mark on the post's icon to show this. Is it an option with this software, or is it just not there? (I don't mind either way – it's more idle curiousity than anything, since by and large the new forum seems better than the old one.)
EDIT: It looks like emoticons aren't getting automatically converted to images (I don't know if it's supposed to be that way or not – it was on the old one, though), and when I've arrived at the editing screen, all of my apostrophes appear munged up – I bet that they'll end up with backslashes after them once I click "Save Edited Post"…
EDIT 2: Or not! How odd that the apostrophes are messed up when editing, then… (I'm using Xubuntu 10.04, with whatever the current Firefox version that their repo carries is.