There seems to be an error in the way the shell figures out how many columns of icons to show in the dash.  I think the dash should always be an integer number of columns wide.  Right now we expect most screens to have a max of 4 but then shrink down if necessary.  However, if you look at the following video you see that when we do shrink down to three the app well is sort of floating in the dash with padding on each side.

http://www.youtube.com/watch?v=BKvRLXLqPI8

Now, this probably isn't helped by having two columns of places and recent items.  And we hope to eliminate that in the next iteration of the design.