Just checked in a couple more changes to keyboard navigation (my specialty). You can now change the focus of the message in the message list by holding down control when using arrow key navigation. It looks great in Firefox, but not so great in IE. If there are any CSS wizards out there that want to take a look at this, feel free. The new class used is in mail.css (#messagelist tr.focused td).
Also there were two bugs that I fixed. The first was that after you deleted (or moved) a message if you used the arrow keys to navigate you would still "select" the invisible message. That invisible message is now properly skipped. The second is that upon moving a message the next message was not selected. It now is.. unless it was the last message in the list. I'll address that ASAP.
-Charles