This is more of an observation than a hint, but I haven't seen it documented anywhere else.
In Snow Leopard, you can now take screen captures while a DVD is playing. In previous versions of OS X, the system would give you an error screen saying that this wasn't allowed. In 10.6, the system will take the screenshot like normal, but block out the DVD Player app window with a checkerboard pattern.
So while this still won't allow you to take screen captures of a DVD (you can use VLC for that), you're now able to at least take screenshots of your screen without being forced to quit DVD Player first. A very welcome refinement.
[robg adds: This behavior has always confused me -- does Apple think consumers are going to take 30 screen captures every second, moving frame by frame over 90 minutes, in order to rebuild the movie from scratch? There are so many easy workarounds for screenshots (VLC, SnapzPro), recording the screen as a movie (ScreenFlow, Camtasia for Mac, Snapz), and just ripping the movie (MacTheRipper, etc.), that it seems really strange to prevent a single snapshot of the DVD Player's screen. In any event, if you want or need a screen grab from a DVD, you'll want to look into one of the alternatives. At least now, though, a playing movie won't block a screenshot of something else on your screen.]
When assigning keyboard shortcuts (on the Keyboard Shortcuts tab in the Keyboard System Preferences panel) for stuff like Exposť (Show All Windows), I always wanted to use shortcuts like Option-Tab or Control-Tab, but these key combinations were not assignable in Mac OS 10.5.
Turns out that they are assignable in Snow Leopard. I assigned Option-Tab to show all program windows (aka Dock Exposť) and Control-Tab to show the Spaces overview. Of course, it's up to you as to what you want those shortcuts to activate.
Please keep in mind that these key combinations may already be used by other applications -- for instance, Control-Tab jumps to the next tab in Safari.
When you have the Open or Save dialog open in an application, you can type the following keyboard shortcut to toggle between showing and hiding the hidden files in a given directory:
If you have your Mac adjusted for a region where the comma is the decimal separator of fraction numbers, or if you are using a keyboard with a comma instead a point on the numerical keyboard, then the shortcut is
This has to be the comma on the numerical keyboard.
[robg adds: This does not work in 10.5, and is one of the more-useful undisclosed features I've yet heard of in Snow Leopard.]
I recently discovered, after trying to change Safari's icon, that Apple's apps in Snow Leopard have read-only permissions enabled for all users except root:wheel. This eliminates users' ability to use copy-paste replacement icons in the Get Info panel.
As a workaround I quit the Finder, and relaunched it as root in Terminal:
I was then able to paste a replacement icon into Safari's Get Info panel. Then, after relaunching the Dock, my icon appeared.
[robg adds: You can quit the Finder using Activity Monitor and it won't restart. If you try this hint, remember to again quit the Finder and relaunch it as your normal user once you're done. I haven't tested this one, so I can't say if it breaks code signing or not.]
If you press and hold Command-Shift-Space Bar, a HUD-style box appears at the center of the screeen and lists available input keyboards. Release and press the Space Bar while holding down Shift-Command cycles through the available choices.
[robg adds: For US users, the default Input Source shortcuts (Command-Space and Command-Option-Space) conflict with Spotlight. I was able to see the HUD panel only after reassigning the Input Source shortcuts; I set them to Option-Space and Shift-Option-Space. The screnshot at right is from my machine; click it for a larger version.]
AppleScripters should re-save their AppleScript .apps in the 10.6 AppleScript Editor so they run in 64-bit mode.
I keep an app on my Finder window toolbar that simply tells Finder to empty the trash; it was so old (having been transferred from previous machines) it may have originally been a PowerPC app. It, and quite a few other AppleScript apps, run significantly faster after I re-compiled them under Snow Leopard.
If you set the folders in your Dock to display using the Grid option, and then click a Docked folder, the contents show and, of course, you can select the items using the mouse/keyboard.
What's cool now is that if you hold the mouse for a second or two on the folder before moving the cursor to the grid area (i.e. don't just click the folder to open it), you get the white highlight to show what item you're mousing over. It's an option that you can choose to use or not -- which is different from the days of on/off in 10.5.
[robg adds: In 10.5, you had to enable this behavior (though it functioned a bit differently) using the mouse-over-hilte-stack preference, as explained in this hint. Now it's always there, but only active if you drag your mouse into the grid area, instead of clicking, releasing, and then moving into the grid area.]
If you are running an installer on a disk image, and you try to eject the disk image, it will tell you that there is an application using the disk image if the installer is currently installing.
But if the installer has not gotten to the installing phase, or if it is waiting for another installer to finish, Mac OS X will let you eject the disk image. Then, when you get to the installing phase, it will fail.
I had always been in the habit of ejecting installer disk images and then, if the installer was running, the system would warn me and I would then know, but it seems that in Snow Leopard that you need to be more careful.
Users who want to run the new 64-bit kernel on late-model Macs (pretty much anything released after early 2008) can do so by booting with the 6 and 4 keys held down. If you're wondering whether your Mac has a 64-bit EFI firmware, you can type this command in Terminal:
ioreg -l -p IODeviceTree | grep firmware-abi
The response will identify the machine as either having 32-bit or 64-bit EFI. I found this tidbit in this article on AppleInsider.
[robg adds: Note that if you boot in 64-bit kernel mode, you may have unexpected oddities. In my case, web pages that contained Flash animations would cause Firefox to quit. Rebooting in 32-bit mode (hold 3 and 2 during boot) solved the problem. Unless you have a definitive need for the 64-bit kernel, I'd recommend sticking with 32-bit mode for now.]