Keyboard Navigation of Snow Leopard's Stacks
If you like using Stacks in Grid view mode in OS X, and you prefer using your keyboard to your mouse, Snow Leopard adds some new keyboard-based navigation ability to Stacks.
As you may already know, Stacks in OS X 10.5 allowed for decent keyboard navigation already. Once a stack is activated (which can be done via the keyboard if you set up a shortcut to switch to the Dock), you can then use the arrow keys to move through the Stack, or you can jump to any item in the Stack by typing the first few letters of its name.
Once an item is selected, press Return to open it. You can even open an item in the background, leaving the Stack on screen by holding down the Option key prior to activating the selected item.
Both of these tricks work in 10.6, but there's a new capability in 10.6's Stacks feature: you can now navigate into Folders while using Grid view in Stacks. Thankfully, this new feature works just as well with the keyboard as it does with the mouse. Just select the folder as you would a file or application (using the arrow keys or letters) and press Return (or Command-O or Command-Down Arrow) to drill down into that folder in a new Stack.
To get back to the parent folder (the one that's actually in your Dock), just press Command-Up Arrow; I find this much easier than finding and clicking the well-hidden arrow at the upper left of the Stack grid.
You can use other modifier key tricks with folders in Grid view Stacks, too. Press Command-Return to open the selected folder in the Finder and close the Stack. Press Command-Option-Return to open the selected folder in the background and leave the Stack open.
I only have a couple of Stacks, but I like that Stacks support keyboard navigation, and find the new drill-down ability to be very useful.