I go on and on (and on) about backing up your computer when going paperless, and for good reason.
I always mention that Mac users have a great built-in option called Time Machine that they can use to back up their important files. It is not infallible, but for a built-in application it is quite good.
A few weeks ago, while walking the streets of San Francisco on the way to the Evernote Trunk Conference, I was listening to John Siracusa and Dan Benjamin’s Hypercritical Episode 82.
In that episode, John made a point which literally made me stop in my tracks: of all the Mac users out there with Time Machine enabled, how many of them actually let it finish and complete the backup?
Now that he has said that, I can imagine a scenario where someone buys a Mac, plugs in an external drive, allows Time Machine to start, and thinks that they are protected from that point forward.
Patience, Anakin
Time Machine can take quite a while to finish, especially on the initial backups. While it should only back up files that have changed, sometimes there can be a surprising amount to transfer. This is especially true if you use applications like iPhoto.
You want to make sure that Time Machine has a chance to save all your changes, because you generally don’t know what specific files it has backed up and what it hasn’t while it is running.
How Do You Know When Time Machine Has Finished?
Your first line of defense is to look at your menu bar somewhere up in the top right. You’ll see your time machine icon. If it is still spinning around, that means it is still running.

If at all possible, you want to wait to shut down or sleep your computer until after the spinning has stopped.
For a bit more information, you can click on that icon, and it will tell you what the status of the latest backup is. Check and make sure that your backup is as recent as you think it is.

Mountain Lion’s Dark Wake
Mountain Lion has a new feature called Power Nap which extends an already-existing feature called “Dark Wake”.
You can read Apple’s page about Power Nap and Macworld has a good summary, but for our purposes, if you are running Mountain Lion on a recent Mac with an SSD, Mountain Lion will periodically wake up the computer when it is sleeping to do some system management tasks.
Thanks to this feature, your computer can actually do a Time Machine backup while it is sleeping. Not bad.
Test, Test, Test
I couldn’t have said it any better than Gabe from MacDrifter did on Twitter the other day:

A key part of any backup, and this is something that I frankly don’t talk enough about, is to test it. Can you actually retrieve the documents that you think are protected?
Give Apple’s Time Machine 101 article a read, and focus on the Restore part.
Your Homework
If you are a Mac user using Time Machine, your homework is to check the status of your backup – has it been running and more importantly, has it been completing?
For bonus points, try restoring some of your most important files. Are you able to?