SpiderOak requires you to use your own password; Jungle Disk optionally offers encryption, in which case you must use your own key. CrashPlan goes a step further, letting you use a public key, which is ostensibly far more difficult to obtain or crack than a password.

Account passwords still remain the weakest link in all but CrashPlan's public key option. If someone can obtain your account name and password, that person can either download client software or use Web sites or locally mounted drives to retrieve your files.

When you need to recover data, most services offer several ways to restore a file or a volume. All but Backblaze let you select files via the desktop software. All but iDrive let you pull down files from their Web site when you're logged into your account; Carbonite only lets you retrieve a single file at a time in this fashion. (Jungle Disk requires its Plus account level for this service.)

iDrive and Jungle Disk also let you mount the backup on the desktop, and you can use the Finder to browse and copy files, folders, or the whole volume.