In the Mountain Lion Reminders app you don't have to click the Inspector button (i) to edit a reminder; just double-click anywhere except on the title of the reminder.
[kirkmc adds: To be precise, you can edit the name of a reminder by double-clicking on it, just like any text in a word processor or text editor. But to display the Inspector window, you have to double-click somewhere in the same line, but not on the text. So you can double-click to the right of its name, if it's short, or if it's too long, you can double-click in the margins above or below it, or to the left of it. You can also click on a reminder and press Command-I to get the Info window. The help says to double-click a reminder, which is not quite true.]
You can create a folder from a selection of files, instead of creating a folder first, then moving files in. In the Finder, select any files you want to put into the same folder. You can do this in any Finder window, including the Desktop or from the results of a Spotlight search (not the Spotlight menu itself). Right-click on any one of the selected files, and the top menu item is New Folder with Selection (number of Items). When you choose that command, a new folder will be created, and the files literally leap into the folder (cute animation!). The new folder is called New Folder With Items, and you can change its name.
[kirkmc adds: This isn't new, it was added in Lion. But it's a nifty thing to be aware of; I use it often. My guess is that a lot of people don't know about it.]
Mountain Lion has added the ability to view multi-page previews of Word documents when you hover your cursor over the icon, as has been possible with PDFs since Lion.
To see a preview, hover your cursor over a Word document. You'll see two arrow icons on the document icon; you can click to the right or left to view different pages.
However, in Icon View, these previews only display if the icons are 64 pixels or larger. They display in Column View, and in Cover Flow View, no matter what size the icons are in the top of the Cover Flow View window.
If you go to the Time Machine System Preference and click on Select Disk, if you already have a disk set as your backup and you select a second disk, you are presented with a dialog asking if you want to delete the current disk or use both disks for Time Machine. You are told that if you us both disks, Time Machine will take turns backing up to both disks. Nice touch to allow backups at work and home to happen at the same time!
[kirkmc adds: This is one of the features that Apple mentioned about Time Machine in Mountain Lion. The backups rotate, and you can either use disks at home and at work, or even two disks in the same place if you are paranoid about backups (as I am).]
With the Share button in Safari on Mountain Lion, you can share web pages using Twitter or Messages. There are no default keyboard shortcuts, but you can create your own.
Open System Preferences, click on the Keyboard icon, then the Keyboard Shortcuts tab. Click on Application Shortcuts, then click on the + icon. Choose Safari as application, then enter either "Twitter" or "Messages" as the Menu Title. Enter the keyboard shortcut you want; I use Command-Control-T for Twitter and Command-Control-M for Messages. Click on Add to apply the shortcut.
Quit Safari and relaunch it. If you click on the Share button in the toolbar, you won't see your new shortcuts, but they work. You can see them by choosing File > Share.
Whenever you want to share a web page via Twitter or Messages, you can now do so with a single keystroke.
If you use Dropbox, you can place symbolic links in your Dropbox folder. This is a great way to backup directories while maintaining the local file structure you desire. As a bonus, the green checkmarks won't display on items backed up in this manner, though they will show up on other computers.
To create a symbolic link, open Terminal, and cd into your Dropbox folder. Then run a command like this. This command would add a symbolic link for a folder called Test that is in your Documents folder:
ln -s ~/Documents/Test
Using symbolic links allows you to add items to your Dropbox folder yet leave them in their "correct" location. So you could, for example, put your entire Documents folder in your Dropbox folder - if you have enough space - yet leave it in its standard location in your home folder.
Also, if you want to back up, say, your Documents folder to Dropbox in this manner, the backup won't take up any extra physical space in the Dropbox folder on your Mac.
I like the new reminders app in 10.8, but I was disappointed to find that there is no way to create new reminders from outside the app (like, e.g., OmniFocus, which has a quick entry window that can be summoned with a keyboard shortcut). I created a service in Automator that allows such entry, albeit with limited functionality.
Create a new service in Automator and choose Service receives no input in any application at the top of the window. Next, in the Text library, choose Ask for Text and drag it to the right-hand part of the Automator window. Enter a prompt, such as "Enter a Reminder." Finally, from the Mail library, choose New Reminders Item and drag that below the Ask for Text item.
Save the service, and use the Services tab in the Keyboard preference pane of System Preferences to add a shortcut that will let you launch this from within any application.
This only allows you to set new reminders in a single list, with a single priority, and with no due date (unless you want everything due on the same day), but it's better than nothing. One more caveat: it's slightly unreliable, because some programs interfere with the Services menu or don't accept Services.
Apps that can access iCloud have a different Open dialog box than we've been used to seeing; the popup menu at the top that lets you navigate up the file path from your current location is missing.
Well, not missing, exactly, just hidden. When you are in the Open dialog, and choose On My Mac, you see the name of the application, then a dash, then the current folder. You can Command-click on the folder name to display a pop-up menu showing the full path for the current folder. There's no visual clue that this is present, but it works.
In Safari 6, when you type into the omnibar - what Apple calls the "address and search field" - the autocomplete menu that shows suggestions for what you typed may be very long. If you want to select your bookmarks or history with the keyboard, you have to press the down arrow many times to get to them.
You can skip sections by holding down the Command key while pressing the up- or down-arrow buttons. So if you've typed something in the address and search field, you can press Command-down arrow to skip past the search engine suggestions, and then use the arrow key alone to select the item you want.
Use a two-finger pinch on a trackpad to zoom the text in TextEdit documents. Pinch your fingers apart to zoom in, and pinch them together to zoom out.
[kirkmc adds: This works zooming in and out with TextEdit. I expected it to work in other apps, and it does in Preview. However, it only works zooming in with Safari; if you pinch together, you see the currently open tabs, as explained in this hint.]