I'm probably too late, but I just found the thread.. I remember Dell coming out with this type of service for their customers. I had to train our staff on how to support it. They called it DataSafe, and had a very simple utility which allowed you to do three things:
1. Browse your hard drive for files to backup
2. Full data restore with the push of a single button (this frightened me for some reason)
3. Subscribe for more storage space on the server and/or more time
Dell allowed you to have 3 Gigs of space for free for the first year after the purchase of a new system, and the software generally came pre-installed. If you liked the service, you'd have to subscribe for preset chunks of space for 1 or 2 years at a time.
Officially, the app was touted as a secure offsite backup service for homeusers and had all sorts of warnings and disclaimers attached to it about connection speeds, which files could be backed up, etc..
Unofficially, the developers over at Dell told us it was a piece of crap management acquired from some tiny little company and told them to stamp on a Dell branding while working out the required infrastructure and a few of the major bugs, and wouldn't recommend it to a red-headed step-child. (I miss those guys.

)
My own opinion? Dell's DataSafe aside, online data backup is a good idea. Like Chicken said, the biggest limit is connection speed. So it really depends on your target market and their likelihood of having a fast enough connection to take advantage of your services. Who's gonna be using this service? Businesses or consumers?
If it's consumers, then your company had better be ready for the barrage of educational calls, customer complaints about functionality, and privacy concerns. We never heard the end of it at Dell On Call, and we weren't even the primary support department for DataSafe.
Other than that, I think I'd use it primarily for storing a weekly system image backup. Two images at a time for consecutive weeks, actually. For each of my hard drives. I'm not too comfortable with the lack of control over the storage media, so it would likely strictly be used as a secondary backup to my primary backup system which would be onsite, like a NAS or
Drobo.
My dad has also been looking for something like this for a while, but so far hasn't really found anything he's comfortable using or thinks is worth paying for.