Imo it's an inconvenience to to be unable to arrange the diagram pane and the text pane in the main editor window side by side vertically (I have quite a bit more horizontal screen real estate than I do vertical). Please allow users to arrange windows as best suits their needs, and to make these arrangements savable.
+1 from me. With multiple widescreen monitors having the panes fixed in their current arrangement is extremely counterproductive when compared to other IDEs -- even good ol' Xselerator (R.I.P.) had a more usable arrangement.