Hi, I'm the CEO of Carbonite and thought I would answer some of your questions.
First, I don't know where the 50GB rumor came from, but it's not true. We have never enforced any limits on backup. Our biggest user is about 300GB. At typical DSL upload speeds of 350kbps, you'll be able to upload about 2.5-3GB per day, so it's really not very practical to backup more than a couple hundred GBs over DSL or Cable.
We do use RAID-6 disk arrays and with several billion files backed up now, but you have to lose 3 disks in an array simultaneously to lose any data, plus your PC has to fail at the same time. While no backup is ever 100%, this is so close to it that most people would not pay double to have a backup of the backup.
Thanks for recommending Carbonite, and if anyone has any questions, please feel free to contact me at david.friend@carbonite.com.
Regards,
Dave Friend