Having a widescreen monitor (1680x1050), it's very nice to be able to use all that space. I note the little arrow symbol on the right side of the main screen to narrow or widen the display space windows. It would be wonderful to have a third option where the main play window is only 100px or so from the left edge and the Local Chat/Activity window is 100px from the right edge. This would leave room for an open Map window that doesn't overlap the game play window.
I frequently play that way to keep track of where I am and where to go. As it stands now, the map window gets overlapped, or I have to move the map window off the edge. The size of the main game play window is fine as it is.