System Preferences: General and Desktop & Screen Saver
Saving and such: Mountain Lion, like Lion before it, has an AutoSave feature, which (in supported applications) will automatically save your changes as you work. Some people found that they didn’t care for this feature as they didn’t want to save the last changes they made before closing a document. When enabled, the first option in this area—'Ask to keep changes when closing documents'—causes a dialog box to appear when you close a document, asking whether you’d like to keep your changes. If you choose not to, the next time you open the document the last version you elected to save is the one that appears (versus the last autosaved version).
The 'Close windows when quitting an application' option addresses another complaint that some people had with Lion: When you restarted an application, all open documents and windows were restored when you next launched the application. Much of the time people want to start fresh rather than with a desktop cluttered with old document windows, and enabling this option makes that possible.
The 'Recent items' pop-up menu is here for no apparent good reason, but it allows you to choose the number of recent documents, applications, and servers that show up when you select the Recent Items command in the Apple menu. Your choices are None, 5, 10, 15, 20, 30, and 50.
Font smoothing: The Mac can smooth the look of fonts using a technology called antialiasing. With the 'Use LCD font smoothing when available' option on, fonts of medium and large point sizes will look smoother.
However, smaller font sizes can be harder to read if antialiasing is turned on. And that’s where the second item in this area comes in. If you find small text difficult to read, turning off antialiasing for just those small sizes can help make the text more legible. It’s within the 'Turn off text smoothing for font sizes x and smaller' pop-up menu that you choose the point size at (and below) which antialiasing is not applied.
Desktop & Screen Saver
The Desktop & Screen Saver preference, as the name suggests, controls two of the more visual functions of the Mac OS. The first is the pattern (called wallpaper in the Windows world) applied to the Mac’s desktop. The second is what the Mac displays when you initiate the Mac’s screensaver. First, the Desktop tab.
Lovely as the picture of the galaxy that adorns your Mac’s desktop by default may be, some people find contemplating such vastness unnerving. Thankfully there’s no need to remind yourself of just how inconsequential your existence is in comparison with such massive and ancient mechanisms. Just select the Desktop & Screen Saver preference, click the Desktop tab, and choose the Desktop Pictures folder that appears on the left side of the window under the Apple heading. To the right you’ll see a collection of lovely Apple-supplied images. As you select an image, the desktop’s picture changes and a larger thumbnail of the image appears near the window’s top-left corner. (Tip: You can drag this thumbnail to the desktop to make a copy of the full-size image.)
If you find the beauty of the images too distracting, select Solid Colors instead and choose one of the default ten colors. If you like the idea of a solid color, but you're not fond of the hues Apple offers, click the Custom Color button to see your old friend the Colors window.
You can also pick images from your iPhoto library and, by default, from the Pictures folder within your user account. (If you’ve installed a copy of Apple’s Aperture photo-editing application, you’ll see an Aperture entry as well.) Click the + (plus) button, and you can use the resulting sheet to navigate to a folder of your choosing. Select the folder in this preference pane, and any compatible images it contains appear to the right.
When you select an iPhoto item or folder, a pop-up menu appears just above the image previews. It’s within this pop-up that you choose how images display as the desktop pattern: Fill Screen, Fit to Screen, Stretch to Fill Screen, Center, and Tile. Fill Screen does exactly that, zooming the image so that it occupies the screen without distortion. Fit to Screen displays the entire image—and where that image doesn’t cover the desktop, a background color of your choosing appears on either side of it. Stretch to Fill Screen stretches the full image so that it covers the desktop. Center places the center of the image smack-dab in the middle of the screen, and may cut off its edges. And Tile takes multiple instances of small images and repeats them in a grid.
Underneath you’ll see three options. The first, 'Change picture', gives the Mac permission to change the desktop pattern every so often—when logging in, when waking from sleep, and at intervals of 5 seconds, 1 minute, 5 minutes, 15 minutes, 30 minutes, 1 hour, or every day. If you enable this option, the second option, 'Random order', becomes active. Switch it on, and the Mac will randomly pick an image. Otherwise, images will change in the order in which they’re displayed.
Finally, Mountain Lion, as did Lion, makes the menu bar translucent so that you can see a bit of a desktop’s image behind it. If you have a particularly busy desktop pattern, you may find this translucence distracting; if so, just disable this option to turn the menu bar an opaque off-white.