Mac 101: Things NOT to do on your Mac

Welcome back to Mac 101; everyone please take your seats, and if you're chewing gum, I hope you brought enough for everybody! Today, rather than suggesting a feature or tool that you might use on your Mac, I'd like to discuss some things to avoid — 5 common Mac-istakes that can stop you in your tracks.

Some quick history: Back in 2006, our own Damien Barrett posted his short list of Mistakes Made by New Mac Users, which drew over 100 responses. Dan Warne did a lovely job summarizing the comments. Recently, Dan Knight at lowendmac.com did a meta-analysis of Dan W.'s list and parsed out what could be easily fixed or made less error-prone. All are useful if you want to avoid some of the most prevalent 'failure modes' for new Mac users, but most of them are simple UI missteps that don't do real damage.
For my part, I don't care so much if people end up with lots of untitled folders on their desktops, confuse the Safari search box for the URL address field, insist on starting every website address with 'www,' or if they refer to Apple Inc. as "Mac" — OK, maybe those are kind of irksome — but I do care if my friends, colleagues or clients put themselves in operational jeopardy with a simple mistake. Here's the list of not-so-smooth moves that cause headaches and aggravation:

1. "Cleaning house." Sure, your Home folder may seem a little bit cluttered... maybe you like your Documents folder inside a "Work" folder, and "Library" doesn't seem that relevant — let's put that in a "Misc" folder! Ah, much... hey, where did all my preferences go, and what happened to my email? Guess what: the default folders that come in a new user folder (might want to give them a colored label to keep track, if you're just starting out) are all there for a reason. Dragging "Documents" to the desktop will break quite a few programs, including Microsoft Office apps, which are looking for a particular "Microsoft User Data" subfolder. Moving "Library" will cause untold havoc. In summary, if you don't know why a folder is where it is, and you didn't put it there, and you don't know what it does, don't move it without consulting a Mac geek; make an alias instead (we'll cover "all about aliases" in future Mac 101s.). As some comments below note, the meta-mistake in this category is to rename your entire home folder; bad bad bad. Many system processes look for the specific paths to your user Library folder (/Users/myname/Library) and if your home folder is renamed or Library folder moved, chances are you'll have trouble logging in.

   Update: A comment asks why it's so difficult to change your username (shortname) in Mac OS X, and shouldn't it be easier and less dangerous to do so? Yes, in principle, you should be free to change anything you want on your account; in practice, Mac OS X links the short account name to a user ID number and lots of other behind-the-scenes configuration bits that are not trivial to change, a legacy of the system's UNIXy and NeXT roots. Most best practice guides for changing shortnames suggest creating a new account and migrating your data rather than trying to change the settings... but if you must change your shortname, Dan Frakes' guide and utility are your best bet.

2. Device disconnects. The "Device Removal" warning sign may be pretty straightforward, but I've seen many iPod and external hard disk users ignore it at their peril. Be sure to eject (Command-E) or drag-to-the-trash any connected volumes before disconnecting your peripherals. Hard disconnects can lead to directory damage and unmountable drives.
3. Hard shutdowns. Second cousin to the abrupt device removal is the hard shutdown, the nuclear option of troubleshooting. In many offices, I've seen Mac users who — just one time — saw a support person hold down the Mac power button to force a shutdown, and from that day forth assumed that the 'proper way' to turn off the machine was with the brute-force approach. Check your Apple menu... there it is... "Shut Down," your friend and mine. The hard shutdown doesn't allow for the regular cleanup and maintenance process of a graceful shutdown; sometimes it's the only option, but it should be reserved for emergencies.
4. Moving Microsoft Office. Any application can be victimized this way, but the Office suite components are most likely to be relocated to the desktop. Don't do it! Aliases, or the Dock, are the best options to have a launchable shortcut for Word or Excel. Moving the actual application will result in a rough day for everyone. (Office apps are looking for other resources in the MS Office folder and will fuss if they can't be located.)
5. Save over, man. It's the easiest mistake to make and one of the most depressing: start a new file. Hit Save. Click on the name of an existing file in the Save dialog, and that name replaces your "untitled" file name. Hit the Save button and (innocently) choose "Yes" when asked if you want to overwrite the existing file. Oops! There goes Mr. Graduate Thesis. I would love to see this feature changed for safety, but in the meantime be aware that this is a great way to lose your equanimity and your remaining hair. Update: Many comments indicate that this is a favorite feature (and, for what it's worth, equally useful/dangerous on Windows). I'd still like to see the Save dialog add a version number or other string by default — maybe an option-click on the filename for an exact match? — but I grant that lots of folks find this more useful than hazardous.