On Mac OS X, when you minimize an application it shows up in the right-hand section of the Dock. If you have a lot of applications open and minimized, this can lead to a lot of clutter in the Dock. Snow Leopard takes care of this clutter with a new option for the Dock that lets you minimize applications into their application icon (on the left part of the Dock) so you don't end up with a lot of extra clutter in the Dock.

To set this open the System Preferences and select the Dock icon. Once it opens, check the box next to Minimize windows into application icon option.

Making this change really reduces the clutter in the Dock.