If you’re tired of having your Dock full of thumbnailed versions of minimized windows, you can change the Dock’s minimize behavior with a simple Terminal command that will minimize windows into the parent applications Dock icon. You can then tell which windows are minimized by looking for the diamond next to the window name (see screenshot). This is very helpful in particular if you’re working with a limited screen resolution, or if you have a Dock that is loaded to the brim with applications and folders.
If you want to enable this feature, launch the Terminal and enter the following command:
defaults write com.apple.dock minimize-to-application -BOOL YES
With how useful this is I’m surprised it’s not an option somewhere within the Mac OS X GUI preferences.