It's not hardware, but the CrashPlan backup software (supporting Linux, too) has a nice way to "backup to a friend". You just have to "friend" each other on the

It's not hardware, but the CrashPlan backup software (supporting Linux, too) has a nice way to "backup to a friend". You just have to "friend" each other on the backup (!) social network and you can select your friend's computer as backup destination and vice versa. While not default, there's an option to not store the encryption key with your account (otherwise there's some escrow going on in case you lose your PC).