Can I add separators in the Mac OS X Dock?

Question

I have placed too many icons in my dock. There is a separator in the Dock between Applications and the Trash.

I want to add more separators in my dock for grouping, to identify groups of icons quickly.

Is it possible? If yes, how?

Solution

From Real separators for the Mac OS X Leopard dock:

Run the following commands from the Terminal:

defaults write com.apple.dock persistent-apps -array-add '{ "tile-type" = "spacer-tile"; }'
killall Dock

Once the dock restarts, you should see a blank space after the last application that is permanently in the Dock (before the icons for applications that are currently running but not always in the Dock).

You can now drag the empty spaces to where you want them, or right-click on them and select "Remove from Dock" if you no longer need them.