MacOS – still set the account picture to an image from disk in OS X Mountain Lion

Administrators don't have ready access to files in other users home directories. Browsing your files would require extraordinary (though admittedly not technically complex) measures and malicious intent.

I'm betting that most Apple store repair techs are a little too busy, and a little too fond of their jobs, to waste a lot of time unlocking and browsing through personal files. There's an old mail server admin adage about being able to read everyone's mail—and not caring. As a consultant I'm "inside" client computers all the time—seeing as little as I possibly can—and I have to tell you, most people's stuff is pretty boring.

I do protect truly confidential data, financial information, CC info, personal photos, inside secure containers such as encrypted disk images, Password Wallet, etc. (In my case this is all in addition to the Filevault 2 protected startup disk.) Having protected the good stuff, I don't lose a lot of sleep about bored repair techs, or interlopers who gain access to my computer, viewing the rest. Your own practice must suit your own position of comfort on the security<>usability continuum, but with a little thought you can get there using the tools the system provides.

The Guest account is enabled in Lion and ML for the Find my Mac feature as it enables the location function for the Find My Mac feature to work. Without the guest account, the location feature will not turn on and therefore will not work.

Disabling the Guest account will effectively disable usage of the Find My Mac feature.