While the next/prev thread buttons are nice and handy, it would also be a plus to be able to move from one message to the next (and back) with a single mouse click. It can get to be kind of tiresome to have to select the next message from the message list in certain cases.

I also think this would help with message navigation.

Perhaps:

"<<" and ">>" for prev/next thread and "<" and ">" for prev/next message.
So the line would look like:

<< < > >>

If you don't like selecting individual messages you can just pick 'flat' mode to get them all
where you just scroll the browser window. The piece that is missing is a flat mode display
of only unread messages on each board. Ideally there would be a button linking to the
parent message if this is a reply to something previous, and from the bottom of the new
messages from one board you would be able to go directly to the same style display of
messages from the next board that had anything new.