Is iPad an autonomous device?
When you buy one, the first thing you see is “Connect to iTunes” screen. You need some “big” computer to start using it. If I’d like to buy one to my grandma, who does not have and cannot use a modern desktop computer, I have no problem with initial setup using my macbook.
The only way to back up your data is, again, to connect to iTunes. Most of the apps keep the data on the server (btw, I hate when people say “in the cloud”), but you still have photos, notes and documents on the device. I don’t know whether MobileMe and iWork.com actually back up the data or just share selected files, but they could be easily extended to do just that later when more people will try to use iPad as a primary device, not just as a “node in a digital hub”. Right now, mobileme offers e-mail hosting which can also synchronize notes. But current version of iPhone OS does not offer notes sync using e-mail account (while Mail.app on Mac OS X does).
If my grandma has a problem with her iPad she might lose her pictures and notes. However, my grandma particularly is not going to take much photographs and notes, so that is not much of a problem.
As of now, the only obstacle to making the iPad an only computer in the house is to get rid of big-brother iTunes requirements by replacing it with a internet service to do the very same thing. I bet Apple is moving towards making iTunes a 100% capable web application in addition to desktop version.