With Exposé's 'all windows' view active, start typing the name of a window to highlight it. Type as much of the name as you like (including spaces and periods) for the desired window. For instance, typing untitled 4 will get you that window instead of untitled 3, etc. Type quickly, though!
After the proper window is highlighted, press Return to make it active and exit Exposé.
While testing this, I once noticed that Exposé didn't register the change of name of a window -- it still registered as Untitled, even though I could see the correct name in the toolbar.
In previous versions of OS X, hot corners would not lock the screen when invoking display sleep, even if the security settings specified it.
The closest thing you could do was to use a screen saver like BlackenedPixels. This, however, was not always reliable for turning off the backlight. Snow Leopard appears to fix this behavior, as it really puts the display to sleep and locks it when you have a hot corner set to activate display sleep.
Should you have a word that you do not want the system to auto-correct (omg is changed to omega, for example), but do not want to permanently add it to the dictionary because it's not a real word, here's a workaround.
In the Language & Text System Preferences panel, click on the Text Substitutions tab, and then put the non-word in both the Replace and With columns. That way, when you type that non-word, it is replaced with itself, and the spelling auto-correction never takes place!
Normally when you Control-click on an item in the Dock, you'll see a contextual menu with that program's Dock commands, along with the OS X system commands (Hide/Show, Quit, and Options). In 10.6, there's now a keyboard shortcut to see just the OS X system commands: hold down Command and Control, then click on an application's Dock icon.
This may not be all that helpful, but it does make closing System Preferences somewhat quicker and cleaner looking, as you don't see all the individual panels in the contextual menu.
[robg adds: If you add in the Option key while holding Command and Control with the contextual menu visible, Quit will change into Force Quit, just as though you had pressed Control-Option before clicking to get the "full" contextual menu.]
I keep the Inputs menu in my menu bar primarily for the Keyboard and Character Viewer functionality. Upon installing Snow Leopard, I saw that the icon for the inputs menu (System Preferences » Language & Text » Input Sources » Show Input Menu in Menu Bar) had changed from a nice colorful American flag (my default input method is U.S.) to a black and white (and ugly) Keyboard & Character Viewer icon.
After a little investigating, it seems that once you select a secondary input method (I chose Australian), the flag icon comes back! The secondary flag shows up when you click on the menu bar item, but you don't need it.
Incidentally, the 'Unicode Hex Input' input method is pretty cool if you want to enter Unicode characters manually (although I find it easier to search for the character I'm looking for in the Character Viewer, and then insert it from there).
There's a new hidden preference available for List view Stacks in the Dock in 10.6. Open Terminal and run these two commands:
$ defaults write com.apple.dock use-new-list-stack -bool YES
$ killall Dock
This will make the List view behave like the Grid view, only with all items arranged in one vertical list, with names to the right.
[robg adds: The screenshot at the right is mine; click it for a larger version of the before (left) and after (right) versions of the List stack. With the change, you'll have to drill down into folders as you do with Grid view stacks; this hint's keyboard method works fine for the new style List view stacks.]
Thanks to this hint (and its original version, appearing as a link to the author's blog in this comment) about using gdb to find hidden preferences, I have discovered that it's still possible to enable automatic mouseover highlighting in stacks as you could in 10.5 (original hint).
It turns out that the name of the preference key has changed from mouse-over-hilte-stack to mouse-over-hilite-stack. So to enable mouseover highlighting of Stacks, open Terminal and run these two commands:
$ defaults write com.apple.dock mouse-over-hilite-stack -boolean yes
$ killall Dock
After that, your Dock's stack items will highlight as soon as you move the mouse over them.
[robg adds: I ran this as a separate hint from the recent Use mouse-over-highlight in 10.6's Stacks as it's been a very popular email request in my inbox, and it struck me that it was worth a standalone entry as the first use of gdb to find a hidden pref in 10.6. Note that it also works in Fan Stacks mode, which wasn't true in 10.5.]
Snow Leopard makes it possible to create keyboard shortcuts to launch applications without using third-party application launchers.
To do so, create a Service using Automator with a single action to launch an application. Set the conditions of this service to receive "no input," and make it available in all applications. Save the Service and create a shortcut to it on the Keyboard Shortcuts tab of the Keyboard System Preferences panel.
Note that the shortcut will not work in apps (Firefox, for one) that don't support Services.
With Exposé's 'all windows' view active, start typing the name of a window to highlight it. Type as much of the name as you like (including spaces and periods) for the desired window. For instance, typing untitled 4 will get you that window instead of untitled 3, etc. Type quickly, though!
