For the last two years, Pogoplug has offered a home-based streaming service that uses local disk storage supplied by end-users and a centralized server to simplify remote data access.
If that sounds like your guess at what the data center and a Time Capsule could accomplish together, you're thinking like we are. Pogoplug doesn't offer any backup capabilities, but it ably moves data between the net and customers on-the-go.
Backup experts Dolly Drive and CrashPlan offer software that takes your OS X backups beyond local Time Machine storage and into the cloud. Both services, along with other competitors, use decentralized passive systems that upload their data in the background. Like Time Machine, users don't have to worry about overseeing regular maintenance. You just set it and forget it.
In use, these services operate slowly and deliberately to back up your data without interrupting normal computer operations.
They don't offer beautiful Time Machine-style interfaces, and there's no streaming component to push data out to the mobile world, but they keep your data safe, especially when "catastrophe" means more than a dead disk.
Now imagine an online music storage locker that can back up and stream your data as well as store your music. Imagine Time Machine extending beyond your Time Capsule hardware and onto the net, with data it can serve regardless of whether your primary Mac is connected or not.
Imagine data that you can access from your MacBook at the coffee shop or from your iPhone at the Doctor's office. Imagine a smart disk drive that knows how to download and cache software updates on its own but also can serve backed up data without you ever having to make it "go."
Apple likes to "surprise and delight" its customers, so Apple's solution may not resemble any of these services. But these existing products certainly inspire some great ideas of where Apple might be pushing boundaries with the iCloud.