Shift+Mousewheel = Pan Vertical
Ctrl+Mousewheel = Pan Horizontal
Ctrl+Shift+Mousewheel = Pan Horizontal

Added keyboard nudge: with object(s) selected, up/down/left/right arrowkeys move selection by one gridpoint.  With no objects selected, arrowkeys pan drawing.  With Alt key pressed, arrowkey nudge/pan moves/pans by 10 gridpoints per keypress.