No matter how good the iPad may be or is, it doesn't replace my laptop! Good try though.
The advantage of the iPad that most of these alternatives lack is that it's light enough to hold in one hand while reading or viewing content.
Look at what happened to the iPhone in 2 or 3 releases. For heaven's sake, Apple was able to establish a game changing ecosystem my then. Extrapolate that for the iPad. There's a good chance that the 3rd generation iPad will be able to subsume 90% of laptop use for almost 90% of the population.
If you want to evaluate the challenge and potential windfall facing Apple with the iPad, then don't compare it to the iPhone. Compare that to the establishment of the App Store.
So while it's not going to be my main device, I certainly see it as being a competitor to the traditional laptop for a MOST people.
Most of all, I think Apple has managed to get the "magic" right once again. I never told my parents that they should buy iPhones, but they did after trying mine, and they are very happy (I'd never thought that my mother would start browsing the web and sending emails, but it's happened thanks to the iPhone).