OS X: If you have a ton of icons and folders pinned to the dock in OS X, this little trick can help you organize them better. With two commands in Terminal, you can add spacers anywhere on the dock to separate the icons.
Open Terminal and copy and paste this command:
defaults write com.apple.dock persistent-apps -array-add '{tile-data={}; tile-type="spacer-tile";}'
Then this one:
killall Dock
The dock will refresh with an added spacer can be dragged to any position (or removed by dragging it off the dock). Repeat the commands to add additional spacers.
You could also use a utility like Dock Designer for more dock customization, but this hidden spacer is already built into OS X. Want even more dock organization? Try arranging the dock like your iPhone homescreen.
This tip comes courtesy of Addictive Tips, which lists many more uncommon OS X tricks.
Mac OS X Tips & Tricks That You Might Not Know About | Addictive Tips