If you paste the link into an application that can recognize it as a link, it will be clickable, and will open the e-mail. For example, TextEdit will display this as a link, if you're using an RTF document. I use BusyCal as my calendar application, and pasting an e-mail link in the Notes field results in a clickable link; however, Apple's Calendar doesn't recognize it as such. The Scrivener word processor recognizes it as a link, but Microsoft Word doesn't.
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.
Copy one of them, paste it at the below those three sections, and add your preferred font and size. Note that you can specify the weight with "-Light," "-Bold," etc. Save the file, relaunch Notes, and choose your new default font from Format > Font > Default Font.
PDF files with horizontal lines and rectangles, but not created as PDF form files, can be filled in as if they were actual PDF form files. Clicking on a line starts a text field the same width as the line. Clicking on a small rectangle toggles a check mark. Rectangles large enough for text entry are not treated as check boxes, but as text fields the same width as the box. After entering text on a line or in a text box, the text may be moved anywhere on the document and retain the formatting. And unlike PDF form files, text attributes as well as text field widths can be changed at will.
[kirkmc adds: I made a test document with Pages, and it works as described. This is pretty neat. I don't know if this is new in Mountain Lion, or if it existed before.]
Safari lets you choose from three search engines: Google, Yahoo! and Bing. You may want to use a different search engine, and Matt Swain's AnySearch Safari plugin lets you do that. It can also turn off Safari's 6's "omnibar" so it doesn't search, and only functions as an address bar.
As a bonus, his KeySearch extension can expand the use of the omnibar to let you search on many sites, such as Wikipedia, Amazon, IMDb, and any site you wish to search, just by using keywords. For example, you can type "wiki Marcel Proust" to search for the Wikipedia page of that author.
Just go to All My Files and the files will show up in their respective categories (or organized another way if you prefer). The path bar for these files lists their location as simply "iCloud." If you don't have All My Files visible in the Finder sidebar, you can add it by going to the Finder's preferences and checking it.
[kirkmc adds: This is interesting, but it's too bad there's no "iCloud" category to find them more easily; they're mixed in with all your other documents. Of course, the whole point of iCloud is that you don't worry about where the documents are…]