First of all, I think you guys have been doing some great work on the new dashboard layout. I especially like seeing the stats. The one thing about the new layout that bothers me is only being able to see a few categories in my category list at a time when I'm making a post.
Since categories are listed vertically, having a really wide box that's not very tall isn't very practical, and tends to cause lots of scrolling every post. With the new layout, there's plenty of available room on the right to have a tall category box underneath the "Publish Status" box, and the layout would be more practical.