I've seen lots of commentary along the lines of "It's doomed to fail because it doesn't have X" (where X is a camera, flash support, desktop-style OS, multitasking support, a hardware keyboard, HDMI output, an open app store, or any of a dozen other features various people consider "must have"). This is wrong. No gizmo can do everything--the question is whether this one does enough.
The iPad isn't intended as (or even capable of being) your primary computing device. It will succeed if it's a more convenient laptop for casual web surfing. It will fail if it's an iPhone which doesn't fit in your pocket.
iPad is a clunky name, but so is MacBook. If it succeeds, nobody will care about the name.
Nine years ago, when Bill Gates announced that everyone would be using Tablet PC's, I don't think he meant "made by Apple."
I have no idea if the iPad will be useful, but for the price I may be willing to take a chance. I've certainly spent more than this on gadgets which didn't meet my expectations in the past. The $500 price is critical in this decision--if it had been $1,000, I would look at it more like a new laptop than a potentially useful toy.
Apple clearly intends to upend the accepted practices of user interface design (practices which Apple was instrumental in popularizing). On the whole, this is a Good Thing, since the desktop user interface is (or has become) far to complicated and technical for a large population of users to properly manage.