^^^
Yeah, that comes in really handy! Also, if you just want to join the upper level with a lower level, just hit Ctrl+E

Some other shortcuts I use:
Ctrl+' = brings up grid or closes it out depending on if it was already on the canvas or not
Ctrl+L = brings up Level window (easier to being up then Brightness/Contrast so I've been using this instead)
Ctrl+A = selects the whole canvas
Ctrl+D = deselects whatever was selected on the canvas
Ctrl+Shift+I = inverts the selected
Ctrl+S = Save
Ctrl+Shift+S = Save As... (<--- every program should have this. I find myself doing this when trying to save documents in other programs)

and that's all I remember for now. C: