This has been around for a bit and I don’t know where it came from originally but I found this over at OS X DailyIn a nut shell it allows you to turn on a highlighting for the stacks feature in the OS Leopard Dock when you hover over them. Nothing more than that but a nice effect all the same.

Highlight Stack Items on Hover

January 7th, 2008 - Mac OS X, Tips & Tricks, Customize, Leopard, 10.5

Here’s a great tip that creates a nice hover effect when your mouse goes over an application (or folder) within a Leopard stack. Why this isn’t enabled by default in Leopard is beyond me, because it makes navigating within stacks a whole lot easier.

Don’t miss out, here’s how to activate it:

Launch the Terminal and type the following command:

defaults writecom.apple.dock mouse-over-hilte-stack -boolean yes

then, you’ll have to restart the Dock by issuing the following command:

killall Dock

To disable the hover highlights, type:

defaults writecom.apple.dock mouse-over-hilte-stack -boolean no

[From Highlight Stack Items on Hover - OS X Daily]