When Spaces is activated (i.e. you're viewing the overview window showing small versions of each Space), holding Command while using the arrow keys to navigate between the Spaces moves any window in the current Space into the new one.
For example, assume the top left Space is showing a Safari window, and that you have this Space selected in the Spaces overview. If you then press Command-Right Arrow, the Safari window will be moved to the top right Space. If there's a window open in that space (Mail maybe), and you press Command-Down, both the Mail window and the Safari window would end up in the bottom right window.
The only reason I can imagine they implemented this behavior would be if someone was trying to collect all open windows into one Space, maybe?
[robg adds: Based on a quick test, it looks like this new Command-Arrow behavior replaces this previous hint, which noted that you could press 'C' in the Spaces overview to collect all open windows. This no longer works in 10.6, nor does 'C' work with any combination of the modifier keys. It looks like there's no longer a 'collect all' shortcut.]
In 10.6, inside an open Stack, you can now dig into a selected folder by pressing Return (or Command-O or Command-Down Arrow) to view the contents of a folder, and then press Command-Up Arrow to go back to the enclosing folder in the Stack. Pressing Command-Return opens the enclosing folder in a Finder window (and add the Option key to open it in the background).
If you use the new minimize to Dock icon feature, and then decide to switch back to the default (minimize to the right side of the Dock), the system won't move any minimized icons from their Dock icons to the right side of the Dock.
Thus, you can have windows minimized both behind application icons and in the right side of the Dock at the same time.
After installing 10.6, I found that the three "special" System Preferences panels (Archives, Disk Images, and Processors) seemed to be missing from the System Preferences panel.
I tried reinstalling from Finder, but when double-clicking on the respective files in Finder, the system told me the panels were already installed. To get them back, I deleted the files in /Library/PreferencePanes (or perhaps in your user's Library/PreferencePanes folder if you installed only for your user). I then double-clicked on the respective files again.
This worked, but the panes can only be installed for all users of the computer. These panels are also 32-bit, as System Preferences will tell you. Finally, I couldn't get the Processor pane to work at all, even after reinstalling it.
[robg adds: I installed the Processor preference panel from the latest Xcode, and it seems to let me control the number of active CPUs, but the option to display the controller in the menu bar isn't working.]
Snow Leopard has a new feature where holding your mouse down on an application icon in the Dock then shows all windows for that application ("application-mode" Exposť). On my Mac, however, I had a problem with this feature and Spaces. If I selected an application window in "application-mode" Exposť for a window located in another Space, Snow Leopard did not move me to that Space, nor did it move the window to my current Space.
I talked with some other users, and none were experiencing this problem, so it seemed particular to my Mac. After changing Spaces' preferences had no effect on the problem, I decided to trash the Dock's preferences file (com.apple.dock.plist in your user's Library » Preferences folder). I then restarted the Dock by typing killall Dock in Terminal (or you could use Activity Monitor).
After doing this, application-mode Exposť works properly for windows in other Spaces -- when I choose one now, I'm taken to that Space, as expected.
I just updated to 10.6, and my printer driver did seem to be supported. Rather than trying to install the old driver, I came across a blog post that said to use a driver from another brand of the same printer.
For my Fuji Xerox Docuprint 203A, I used the Brother HL-2030, which has the same printer icon and setup. This worked perfectly for me.
[robg adds: I can't easily test this one here, but you'll want to do some preliminary work with Google to find out if your printer is available under different names from other companies.]
This may or may not work in all situations, but if you are struggling with opening a video file using the new QuickTime Player in Snow Leopard, this may help you.
I have found that Quicktime X has a little bit of an issue with opening video files that have an AC3 soundtrack. When I attempt to open a file with an AC3 soundtrack, QuickTime will state that "The document could not be opened." These files work without an issue in QuickTime 7 on Snow Leopard, so I know the files are fine.
The solution to this issue is to open the file in QuickTime 7, remove the AC3 soundtrack from the file, and then re-save it. That way, you will be using the stereo track for your sound (should it exist). You can do this by going to the Window » Show Movie Properties dialog and deleting the AC3/Surround track, and ticking the box beside the Stereo track. Re-save and you should be able to open in QT X.
In the Language & Text System Preferences panel, on the Text tab, you can enter text to be replaced with symbols/longer text blocks - just click the Plus sign to enter a new substitution.
The hint here is that you can have it enter in new lines by using \n (backslash n). This is especially useful for email signing, as you can have something like rjs expand to:
[robg adds: Separately from this hint, Mac OS X Hints reader HairyPotter points out that you can enter your text in TextEdit (or other editor), then copy and paste it complete with line breaks in the Text tab. I also discovered you can force a new line by typing Option-Return directly in the Text tab.]