Not sure why anyone would want to backup anything in the cloud. Backups should be kept local, secure and readily accessable. You can always use two external disks for Time Machine (effectively creating two backups) and manually swap between them in the Time Machine settings panel (Settings>Time Machine>Select Disks).
If you are really intent on backing up to the sky, check out DollyDrive. They offer a service that will enable you to backup your Time Machine in the cloud. Their standard plan gives you 250GB of storage and will run you $96/year; their delux plan gives you 1TB and will run you $288/year.
Message was edited by: ou812ManySushi
I have looked at a LOT of backup software for the OS X and based on what I see most are designed to backup the machine, but not an external attached drive.
Suggest that you look at applications that are capable of backing up a network drive to another drive. That would be Chronosync or Carbon Copy Cloner.
As you might imagine, the "free" or "demo" version of these applications will not provide the features that you need.
I'm not sure why anyone would want to backup their important or personal files to someone else's hard drive....but that is what you are doing when you backup to the "Cloud".
The big advantage to a cloud back up is having it off site. I agree that your primary back up should be local and available, but in the event of a catastrophe your local back ups would also possibly be destroyed. A fire or a flood could easily destroy just about everything electronic in your home.
I back up to a Time Capsule, which is a great everyday back up solution. Three years ago my home was hit by lighting, and it destroyed just about every piece of electronics in my home including my Time Capsule and every computer. Having an off site back up was all that saved me.