If you leave certain applications running without any open windows, OS X will quit the application when it goes to the background. This happens with some Apple apps such as TextEdit and Preview, and perhaps others. There is no user setting to change this in preferences. Here is a Terminal command line to change this feature:
[kirkmc adds: What's interesting is when OS X kills an application using this feature, the app still shows up in Activity Monitor. Matt Neuberg has a good overview of this at TidBITS. This has been around since Lion, and I'm surprised there hasn't been a hint yet. The submission specified Mountain Lion, and it's possible that this "feature" is more aggressive in 10.8, but I found mention of this command from before Mountain Lion.]
Arrow keys now allow you to move through events in Calendar. If you select one event, you can move around through all your events by using the arrow keys. Note that you can't highlight an all-day event using the arrow keys except in Month view.
Another behavior that might be new: if you hold down the Control key, a left or right arrow key will move a highlighted event right or left across days and the up/down keys will move the event in 15-minute increments when you are in Day or Week view, or move it up or down the calendar in Month view.
[kirkmc adds: Is this new in 10.8? I don't use iCal; um, Calendar.]
In Safari 6, with the new combined URL and search field, if you type search terms into the field, then press return, you'll get a Google page with the results, but you won't get a search URL in the address field. Some people want to save searches at times. Macworld's Dan Frakes tweeted an AppleScript which does just that and Many Tricks developer Peter Maurer improved on it. Run the script and it will get the URL for the frontmost tab then send it to the clipboard, from which you can paste it where you want.
tell application "Safari"
set the clipboard to URL of current tab of window 1 as string
As Dan Frakes later pointed out on Twitter, you can also drag the favicon to a finder window. You can double-click the resulting file to redo the search, or you can press the Spacebar to Quick Look it and see a live search with clickable links. For a search, the favicon is the magnifying glass icon at the left of the search field.
So, how many other ways can you find to save a Google search URL?
Update: Jordan Kay posted an even shorter version on Twitter:
tell application "Safari" to set the clipboard to URL of current tab of window 1 as string
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.
If you have multiple conversations visible in Messages, you can cycle through them using a keyboard shortcut: press Control-Tab to cycle down, and Shift-Control-Tab to cycle up.
There seem to be some inconsistencies. When testing this, if I had my cursor in the text field, sometimes the keyboard shortcut wouldn't work and would instead highlight the name in the To section above the conversation.
After installing Mountain Lion, I was looking for an easy way to convert the e-mails I receive into reminders to act on later. After trying in vain in Mail (right clicks, menus, etc.) I found the solution is simple.
Just drag an e-mail from Mail to Reminders and a new Reminder is automatically created with the subject of the e-mail as title and a link to the e-mail in the notes.
[kirkmc adds: To be honest, I expected there to be a clearer way to do this: a toolbar button in Mail, or a contextual menu item. I think a lot of people - like me - use their inbox as a to-do list. Being able to add them to the Reminders app can be very useful.]
Apple removed the default font settings preferences in Safari 6, but one can easily change them with a set of Terminal commands. More fun, though, is using TextExpander's Shell Script Snippet feature to do it. Slight advantage: once the snippet is in your collection, you can edit the snippet to change the fonts at any time without having to dig up the commands from your memory. Note that you have to quit and restart Safari for the changes to take effect.
Update: The submitter, Michael Cohen, wrote me saying that his brother Norman Cohen improved on the above script. I'll leave the original there, but below is a newer version, where the script quits and restarts Safari, and using TextExpander's fill-ins, lets you specify the fonts and sizes on the fly:
Since Mountain Lion was released, I find that my Macs go to sleep when I don't want them to. I had my Energy Saver preferences set to 15 minutes, but I've noticed that when something is active, such as a download, they got to sleep after 15 minutes, rather than continue with the download. This is not only incorrect behavior, but it's very annoying. What's worse, when I changed the setting to Never, they would still go to sleep during long downloads.
The Ask Different blog pointed out that there is a new command in Mountain Lion called caffeinate. This keeps the system awake, or, as the man page says, "prevent the system from sleeping on behalf of a utility."
Run it as follows in Terminal:
caffeinate -u -t 3600
3600 in the above command is the number of seconds to keep the system awake. What's interesting is that you can effectively set your Mac to shut down at a specific time (that is, the built-in sleep mechanism will start counting when that time runs out). You can also run the command alone to keep your Mac awake until you stop it by pressing Control-C.
So Mountain Lion has been out for a week, and a lot of people who read this site have developer accounts and have been using it for longer than that. What do you think of it? The best version of OS X ever? Needs more work? A total failure?
For this poll, you get to play teacher and give Mountain Lion a grade. Pass or fail? Vote here.