[john.gersh]

Here's a quick and dirty Applescript for setting zoom globally. It's true that the script-accessible zoom is a property of the window, though canvasas obviously retain a zoom level. This script just asks for a new zoom level (default is the current one) and then cycles the canvases through the window to set their zoom level.

tell application "OmniGraffle Professional 5"
	set currentZoom to the zoom of the front window
	set theDialog to display dialog "Zoom all canvases to:" default answer 100 * currentZoom
	set theZoom to the text returned of theDialog
	set currentCanvas to the canvas of the front window
	repeat with theCanv in every canvas in the document of the front window
		set the canvas of the front window to theCanv
		set the zoom of the front window to theZoom / 100
	end repeat
	set the canvas of the front window to currentCanvas
end tell