It’s a simple thing to change ⌘-H in Photoshop to hide the app, bringing it in line with other Mac apps, but most people don’t know how. (By default it hides guides and other things.) Adobe’s going to rectify this in CS5 by giving a choice to the user on first launch. Nice move.
(To do this in CS4, go to Window -> Workspace -> Keyboard Shortcuts and Menus. Next to “Shortcuts For:” select “Application Menus”. “Hide Photoshop” is there and can be changed to ⌘-H.)