In iOS, whenever you view a document attached to an e-mail, you can click the Share button to send the document to a list of compatible applications, not just the preferred one. The same option is available in Mountain Lion whenever you use Quick Look to view a document.
When you display a document using Quick Look, you can now right-click on the "Open in xxxx" button, and see a list of compatible applications. This makes it easy to open, for example, a spreadsheet or graphic in your application of choice instead of the default application.
If you've tried burning the Mountain Lion installer to a standard DVD, you've probably noticed that it does not quite fit. Fortunately, there is a way around this.
The problem is that the size of the InstallESD image is fixed at 4.75 GB; slightly larger then a 4.7 GB single-layer DVD. However, the actual contents of the image occupy only 4.38 GB on disk, which will fit on a standard DVD.
In order to cram Mountain Lion onto a standard DVD, we need create a slightly smaller image file of the exact same format, copy the contents over, then burn it to a DVD.
I've written a small script to make this process quick and easy. Simply paste the code below into a plain text document and save it with a file extension of ".sh" To run the script, fire up Terminal and enter "bash /path/to/script.sh". When this script finishes, you will have a new, smaller DVD image in your home folder, ready for burning.
NOTE: This script assumes you have the "Install OS X Mountain Lion" application in /Applications. It won't work if it's located elsewhere. You'll also want to make sure you have at least 9 GB of disk space free, as the script temporarily creates two additional copies of the install image.
rm -f /private/tmp/Mountain\ Lion\ DVD\ Image\ read-write.dmg # Remove any old copies of the DVD image before we begin.
echo "Creating DVD Image..."
hdiutil create -size 4.2g -volname "Mac OS X Install ESD" /private/tmp/Mountain\ Lion\ DVD\ Image\ read-write.dmg -fs HFS+ -layout SPUD
# hdiutil attach -nobrowse /Applications/Install\ OS\ X\ Mountain\ Lion.app/Contents/SharedSupport/InstallESD.dmg
hdiutil attach -nobrowse ~/Desktop/InstallESD.dmg
hdiutil attach -nobrowse /private/tmp/Mountain\ Lion\ DVD\ Image\ read-write.dmg
echo "Copying Mountain Lion to new image..."
cp -pRv /Volumes/Mac\ OS\ X\ Install\ ESD/* /Volumes/Mac\ OS\ X\ Install\ ESD\ 1/
hdiutil detach /Volumes/Mac\ OS\ X\ Install\ ESD\ 1
hdiutil detach /Volumes/Mac\ OS\ X\ Install\ ESD
echo "Converting to read-only..."
hdiutil convert /private/tmp/Mountain\ Lion\ DVD\ Image\ read-write.dmg -format UDZO -o ~/Desktop/Mountain\ Lion\ DVD\ Image.dmg
rm -f /private/tmp/Mountain\ Lion\ DVD\ Image\ read-write.dmg
echo "Image Creation Complete. Please burn '~/Desktop/Mountain Lion DVD Image.dmg' to a DVD using Disk Utility."
[kirkmc adds: I haven't tested this. Given the cost of USB sticks, and the fact that, if you do want an installer, it's better to have the most recent one, I've gone that route using Lion DiskMaker. Some people may prefer DVDs, but another factor is whether or not your Mac has an internal DVD drive; my Macs - a Mac mini and a MacBook Pro - do not, so USB is easier than using an external drive.
Note: I've updated the script in the hint to the last revision below in the comments as of 8/18/12.]
I discovered while adding some new Mail rules that existing rules which ran an AppleScript seemed to be missing the scripts I had designated, even though they were still in my Scripts folder (~/Library/Scripts). Upon clicking the "Open in Finder" option in the drop-down menu for choosing an existing AppleScript, it took me to a new file path: ~/Library/Application Scripts/com.apple.mail.
You just need to copy or move the scripts to the new folder. Mail seems smart enough to remember the earlier choice and update the rules by moving the scripts to the new folders.
[kirkmc adds: This probably has something to do with sandboxing. The only other application I use AppleScripts for is iTunes, and their location hasn't changed. Can anyone post in the comments if they see other folders in the Application Scripts folder?]
Migrating Mail from Lion to Mountain Lion leaves behind a folder containing previous attachments.
Attachments in Lion were saved to ~/Library/Mail Downloads, but under Mountain Lion, Mail is now sandboxed, and the new path is ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads.
During the upgrade, the folder contents are copied from the old location to the new, so the old location can be deleted to save some space.
[kirkmc adds: While this may not save a lot of space, if you get a lot of e-mail with attachments, you may have plenty of files in that folder. I clean mine out from time to time, so it's good to note the new location.]
If you go to LaunchPad, you can search for apps by typing a couple of letters. You'll see a search field at the top of the window. You don't need to move the cursor there; you just start typing. Launchpad will narrow down its list of apps to those named with the same initial characters as any typed text. For example, "pre" will return Preview, whereas "rev" won't.
Additionally, it returns apps that contain capital letters and words' initial letters from any consecutive position within their names that match the typed text. So, "qt" will return QuickTime Player, "sp" will return System Preferences, and "p" will return iPhoto.
[kirkmc adds: It seems that LaunchPad treats capital letters at any location in an application name as important, just as Spotlight does.]
In the new Reminders app, you can select several reminder lists by clicking on one, then Command-clicking on others. When you do this, the reminders will all display in one window, with a header saying, for example, 3 Lists. A smaller header will show the name of each list, with each reminder under the header for its list. If you then click the Hide Reminders button at the bottom-left of the app, you get a very neat reminders app that shows all non-completed tasks in a single list.
I found that the RSS Visualizer screensaver still works if you reinstall it from a copy of Lion.
In a Lion backup, if you still have one, go to:
/System/Library/Screen Savers/RSS Visualizer.qtz
Copy it to:
on your Mountain Lion Mac.
[kirkmc adds: I haven't tried this, but there have been other submissions about copying screen savers from Lion to use in Mountain Lion. If you're missing your favorite system screen saver, and have a Lion backup, it's worth checking to see if it will work in Mountain Lion. Personally, I'm still using the Basic Black screensaver.]
I saw this early on in Mountain Lion, but forgot to add it as a hint (and I'm surprised no one has submitted it yet). One of the interesting features in 10.8 is the ability to rename files from the title bar. To do this, hover your cursor over a title bar, then, when the small downward-pointing arrow displays to the right of the name, click on it and choose Rename... The name in the title bar will become highlighted, and you can rename it.
(H/t OS X Daily whose post reminded me to post this hint.)
There is a gesture you can use on a trackpad to view Notification Center: swipe with two fingers from the right edge of your trackpad to the left. This works on a laptop, but with a Magic Trackpad, this really isn't easy to do, since your fingers can't slide from a surface next to the trackpad. All it generally does for me is move my trackpad to the left. (And if you happen to use the Magic Trackpad with your left hand, I'm not sure what would happen.)
So what I did is set up a hot corner on my desktop Mac, the one where I use the Magic Trackpad. To do this, go to System Preferences, then Mission Control. Click on the Hot Corners button, then choose Notification Center from one of the menus; the one for the corner you want to use. So I have it set to the top-right corner, which is logical, as that is where Notification Center lives. I just move my cursor to that corner and the Notification Center sidebar displays. To hide it, I just click elsewhere, or move the cursor to the same corner again.