If you hold down the Command key while dragging an icon to a Terminal window, it will cd to either the directory you dragged (if it's a folder) or the directory containing the item you dragged (if it's a file).
I don't know when this feature appeared; it might not be specific to 10.8, but that's where I discovered it.
[kirkmc adds: This is a really neat feature. Also, if you Command-drag an application or other bundle, Terminal will cd to inside that bundle. This is great if you need to access files within an application bundle, for example. The comments are saying that this is indeed 10.8 only.]
Mountain Lion removes RSS functionality from both Mail and Safari. To facilitate the transfer of your feeds to another RSS reader, you can collect the feed URLs by running the following script in the ~/Library/Mail/V2/RSS directory of your latest backup.
Go to: ~/Library/Mail/V2/RSS/ in your latest backup.
Run the following in Terminal: find . -name "Info.plist" -exec grep -A 1 Feed {} \; | grep string | sed 's/^[^>]*>//' | sed 's/<[^>]*>$//'
[kirkmc adds: I never used RSS with Mail or Safari so I don't see anything there.]
With Mountain Lion, you can now use the OS to encrypt disks other than the startup volume, assuming they are in GUID format. This includes USB flash drives and external Firewire/USB/ThunderBolt drives.
In the Finder, open a new window. Find your mounted (GUID) drive in the sidebar.
Control-click on the drive in the sidebar, then choose "Encrypt <drive name>." You are now prompted for your password and a hint (which is required). You will get no feedback, so wait for a few minutes; the time depends on the size of the drive.
The drive should unmount and mount again. Once this happens, your drive is encrypted.
If you choose your startup volume, this will enable FileVault II. Other drives do not enable FileVault II.
[kirkmc adds: I, for one, think this is pretty nifty. I know a lot of people who have two drives in an older laptop, where they replaced the optical drive with an SSD. Being able to encrypt the non-boot drive is quite practical, and being able to encrypt a portable drive even better.
It should be noted that there's no feedback during the encryption process. The only way you know something is happening is if the drive has an LED that shows read/write activity. And the process can take a long time; even for a 1 GB flash drive, where I tested it, it took several minutes.
Another thing to note is that an encrypted drive doesn't show up in Disk Utility. So if you need to erase that drive, you have to right-click on the drive's name and choose "Decrypt <drive name>."]
I deal with a lot of PDF documents and until now was using Lion. I used to Quick Look PDFs all the time, and pinching used to make it full screen. But even in full screen, because most document have a portrait orientation, many times the text wasn't readable enough. Now, pinching in Quick Look, both normally and when full screened, zooms in or out like in Preview. I've tested this only with PDFs. I tried with a JPG, and pinching did nothing to it.
[kirkmc adds: Yes, I get this to work with PDFs, but not with other graphic formats. ]
If you haven't noticed, Web Sharing has been removed from Mountain Lion. According to Apple, if you need Web Sharing, you should probably look at OS X Server.
Nevertheless, many people want to use Web Sharing, notably to run a local server to test win site design. I've come across two tutorials. One by Brett Terpstra and another by Neil Gee. Finally, Tyler Hall has created a Web Sharing preference pane
Personally, I don't need Web Sharing generally, but I have used it in the past to test web applications. So if you need it, check out the above links.
The email a link command in Safari seems to have disappeared, but it's actually just hidden behind a keyboard shortcut. Command-Shift-I opens a new email with a link to the current page in Safari.
To play your Mac's audio over an AirPlay device (like an Apple TV or AirPort Express), the standard way is to open System Preferences, then click on the Sound pane, then the Output tab, then select the device.
There's a much quicker way, however. If you have the Volume menu visible in the menubar, clicking on this icon displays a simple volume slider. But if you hold the Option key when you click on the icon, you can select audio inputs and outputs directly, including nearby devices compatible with AirPlay.
[kirkmc adds: This isn't new, at least the part about using an Option-click to choose input and output devices. It's worth pointing it out again, however, because you can now choose AirPlay devices as well from this menu. As noted in the comments below, it seems that this menu only displays the last selected AirPlay device.]
Mountain Lion introduced a new Open dialog to reflect iOS behavior. This dialog appears in TextEdit and Preview when you launch them, and you can't disable it in the applications' preferences.
The only way to disable the iCloud open dialog is to uncheck Documents & Data in the iCloud pane of System Preferences. This also disables the default iCloud destination in Save dialogs.
Previously, if you had the iChat File transfers window open, you could click on an inline graphic that someone sent you in a chat and press the space bar to view it in Quick Look. In Mountain Lion, this no longer works. You can, however, click on the graphic in the Messages window, then press the space bar to view the image in Quick Look.
