It's not paranoid to worry about your backup data being intercepted, or being retrieved by other parties from your hosted storage area. Each storage company has various security protocols in its software, on its servers, and in its companies to prevent access to data. Nonetheless, it's a legitimate concern.
All services except iDrive and Jungle Disk first encrypt data on your computer using their software, whether it's the first backup of a file or an incremental piece. Most services then use 128-bit SSL/TLS, the same encryption used for secure Web transactions to transfer data. In iDrive's case, the company uses the SSL/TLS transfer, and then encrypts data when it arrives on the server. Jungle Disk uses secure transport, but makes file encryption optional. (There are no known cracks against 128-bit SSL/TLS, and any discovered would affect all e-commerce and banking transactions worldwide.)
Backblaze, CrashPlan Central, Mozy, Jungle Disk, and SpiderOak all offer one additional level of paranoia: you can set your own password to encrypt files on your computer. The service then has no idea what your password is, and no cracker, government agent, or other party can decrypt your files. Lose this key and, just like an encryption key used with desktop password software, you're hosed. (iDrive says it plans to add a password option to its Mac software.)
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.
While each service, except Carbonite, offers some kind of archive of older versions of each document, only a few make it easy to pick which version you want. Backblaze makes you select a snapshot date from a pop-up menu to access versions, and the same is true of Mozy. CrashPlan, by contrast, has an expand triangle next to files that displays each version by date.
Downstream rates seemed to be constrained more by the time a service took to piece together restored files, sometimes instantly, sometimes with long but reasonable waits, than by bandwidth.
To make sure everything is running smoothly, set yourself a remember to periodically test retrieving a moderate set of files, perhaps 100 totaling a few gigabytes, to make sure nothing's wrong at the far end that's gone unnoticed.
And for safety-sake, you should also back up at home using Time Machine or another method. If an online storage site goes belly-up or fails to pay its hefty bandwidth bill, you'll want to be protected.
For some people, opting for Jungle Disk's well-financed Rackspace or S3 servers offers extra peace of mind.
Price is always an issue, coupled with ease of use. CrashPlan gets the highest marks for interface design, simplicity, options, and cost for two or more computers. CrashPlan also adds desktop and personal remote backup (to other computers you own or to those of your friends) in the same software at no extra cost. (An upgrade to CrashPlan+ adds a handful of features for desktop backup.) For those who want to mount a backup drive locally, who want more precise control over every tiny aspect of backups and who have relatively small backup sets, Jungle Disk provides odd software but all the options you could ever need. For 50GB of stored backups, the cost is $7.50 (£4.50) in storage; for truly large backup sets, an unlimited option is the only choice.