Can I force Snow Leopard to open new windows on my primary display?

"There is not any way to do this except closing a window on the monitor that you want the next window to open on--as you have realized. This is a feature, just not for you! You mention SizeUp which is the best solution to manage windows on multiple monitors in my opinion as it lets you assign shortcuts to move windows between monitors. With SizeUp you can move a window between monitors even if it is behind a full screen movie for example, as long as the window you want to move is the front most window of the active application.

I also make heavy use of Hiding applications rather than dragging them out of my way onto my second monitor, and I have transparent icons in the dock so I can see what I have hidden. When I command tab back to the hidden app it's windows are right where I want them to be."