When switching from Design Mode to User Mode or Custom Menus Mode it is sometimes desirable to hide all windows in the Design environment (e.g. open methods and forms) without permanently closing them. There is a keyboard shortcut for this.
When in the Design environment, hold down the SHIFT key and select either User or Custom Menus from the Mode menu. This will hide all of the Design environment windows.
You can also hold down the SHIFT key while using the Mode keyboard shortcuts (e.g. CTRL+U).