In OS 10.0-10.2, there was no sidebar in Finder windows and commonly-used locations were chosen by clicking on an icon in the toolbar. When Apple added the sidebar in 10.3, they changed the functionality of both the sidebar and the toolbar so that it 'roots' you to whatever location you picked while in column view, i.e. removes the horizontal scroll bar so that you can't access lower-level directories.
There were only two ways around this: double-clicking command-up arrow, or using this hint. In Snow Leopard, the functionality of column view has changed again. Now, when you have the sidebar visible, it still roots you to that spot. However, if you have the sidebar disabled (View » Hide Sidebar), clicking on an icon in the toolbar still gives you access to the entire file hierarchy with a horizontal scroll bar!
It's great; Apple finally let us reclaim all that unused space in the toolbar and gave us the ability to get rid of the sidebar by default (which is not an efficient use of space). It's a little buggy though, in that if you are previously rooted, you stay that way until you click on a lower level directory.
Incidentally, I'm typing this on the 13" MacBook Air, having previously had a 15" MacBook Pro and let me tell you, having the extra screen real estate without that sidebar there is great.
After several failed attempts to connect to iDisk in 10.6 (e.g. poor internet connection), Finder tends to crash with the error:
The application "Finder" cannot be opened
Finder then will not automatically restart. But there is a fix if you have Spotlight, Quicksilver, Google Quicksearch box, or some other access to Terminal. If you do, launch Terminal and type killall Finder, then press Return. Finder, although apparently not an active process (per the above error), will then restart immediately and successfully.
The following is more of an undocumented change than a hint.
In Finder's Column View (where I spend the vast majority of my time), if you use Select All (Command-A) with a folder is selected, previous releases of OS X would highlight the entire contents of the selected folder. In 10.6, I am seeing the behavior change to selecting the entire contents of the folder in which the selected folder resides.
This actually makes more sense because it is consistent with Select All used on a non-folder item, but it's going to take me a few days to re-calibrate my brain and fingers.
[robg adds: In testing this, I noticed that the behavior differs depending on how the folder is selected. If you select a folder with the mouse and then press Command-A, the behavior is the same as previous versions of OS X. But when you use the keyboard to select a folder, pressing Command-A highlights everything at the same level as the selected folder. I'm would think one behavior or the other is a bug; it seems they should be consistent.]
I was very disappointed that I couldn't add the Size column to the list view in search results in Snow Leopard like you could do in Tiger, since Apple gave us the impression that Spotlight would include additional ways to sort results in Snow Leopard. Only Date Created and Date Modified were added as options in 10.6; the others are grayed out.
Fortunately, I found a way to force the Size column to appear, as well as Comments, Version and Label columns. You'll have to edit the com.apple.finder.plist file found in ~/Library/Preferences, using the Property List Editor app (included with Xcode) or PlistEdit Pro.
Open the Root node, then navigate down into SearchViewSettings » ListViewSettings » columns. Then choose the column you want to activate in the column list (ie. Size), and set the visible key to yes. Save the .plist and relaunch the Finder (Option-Control-click on the Finder icon in the Dock).
Note: you must have done at least one search, and selected one of the additional columns in the View Options panel for the search results (Date Created, for example), or else your .plist file may not contain the SearchViewSettings node.
Warning: Apple probably disabled these columns for a good reason, as there may be some bugs that could cause problems on your system. I didn't have any problems with the size column, but be warned.
[robg adds: I have no idea why it's taken over three years (and counting) to fix something that worked in 10.4. Until Apple gets it fixed, though, this seems to do the trick. I tested it on my MacBook Pro, and haven't had any problems as of yet. Note that you won't be able to actively enable/disable the columns in the View Options dialog, but all the columns you set to yes will show in your search results -- and once they're showing, you can sort as expected by simply clicking a column heading.]
This has been mentioned before, but given that this just relieved the woe of a colleague who had upgraded to Snow Leopard, it is perhaps worth mentioning again:
If Finder seems to routinely "hang" or stop responding, deleting the Finder preferences file (com.apple.finder.plist) in ~/Library/Preferences, and subsequently restarting the Finder (using Terminal, Activity Monitor, etc.) may solve your problem.
Here's a workaround to making a Smart Folder stack. You can probably use Folder Actions to accomplish this in Snow Leopard, since Apple added the Date Created option to Spotlight search. I prefer to use Noodlesoft's Hazel, however.
Create a new directory and subdirectory for handling your Hazel-driven dock stacks. (~/SmarterFolders/New Applications). I made SmarterFolders to contain New Applications, the folder which will later be a stack of its own.
Create the first Hazel rule for the /Applications directory, and make it look like this. The Growl notification reads: File is new. An alias has been created in New Applications.
All Conditions met:
Date Added is Today
Comments do not contain NewApp
Do the following:
Make Alias in New Applications
Send Growl notification: file is new. An alias has been created in New Applications.
Add Comment "NewApp"
Create the second Hazel rule for the ~/SmarterFolders/New Applications directory, and make it look like this. The Growl notification reads: file is 2 weeks old. Alias has been moved to Trash.
Date Created is not in the last 1 Week
Do the Following:
Move file to Trash
Send Growl notification
Make sure you check Delete duplicates in the Hazel menu screen for the New Applications folder.
Drag New Applications to the Stacks area of the Dock. Change your settings as desired.
Clipping files in Snow Leopard have gained significant features. First, they now work with Quick Look. Second, you can open a clipping file and actually select a portion of the text to copy. Finally, they have a fully-functional title bar, so you can Command-click (or Control-click) the title to see the full path.
[robg adds: In 10.5, you actually could copy text from clippings, but the selected text didn't highlight, making it very hard to use this feature.]
As pointed out in this truly ancient hint, if you have multiple Finder windows open, Option-clicking the minimize (yellow) button will send all of those open windows to the Dock. No big deal hint there.
However, now with Snow Leopard, Option-clicking on any docked window will now release all docked Finder windows.
[robg adds: In 10.5, Option-clicking on one of many docked Finder windows didn't do anything, whereas it did work for docked windows from Firefox, TextEdit, and other apps.]
I noticed the Finder was consuming all of my memory and 40% of my CPU power. I found this reproducibly occurs if you leave a window open in /tmp, and have it set in Cover Flow view mode. When looking at /tmp, memory and CPU usage is higher than normal in other views as well, but Cover Flow really spikes it.
The CPU usage is not a bug, it's simply the Finder having to rapidly update the icons of the transient files flickering in and out of /tmp. As for the 3.5GB of memory usage, while this might indicate some sort of memory leak, I'd also guess it might instead be some sort of too-aggressive Finder caching that's unsuited for the transient directory behavior. (It takes a long time for the Finder to soak up all that memory, but the CPU effect is instant.)
So the hint is: don't view /tmp in Cover Flow view mode!