With the iPad, if I want to be able to use it whenever I need it, I would have to sacrifice the use one of my hands carrying it around for almost every waking hour. No-one is going to do that. People don't carry netbooks around with them 24/7, even though having access to a netbook 24/7 would be handy. It's just too much of a hassle to have something in your hand all the time.
People do carry their iPhone with them 24/7, though, because when not in use, you can stick an iPhone in your pocket or on a belt clip and it is, for all intents and purposes, gone. The iPhone is a success because it's a crappy computer that's there whenever you happen to need it (even when you're not expecting to need it). That's a killer combination. The iPad is a crappy computer that won't always be there when you need it. Dead in the water, baby.
While the iPad is smaller than most laptops and even netbooks, if I have to carry it in a backpack or briefcase, it's just as unpocketable as any other laptop or netbook. That makes it a netbook, regardless of what uncle Steve says.
So the question becomes, how does the iPad stack up against other netbooks and laptops (especially considering that you can get a pretty kickass laptop for $500 nowadays and carriers are giving away netbooks for free with service contracts). Lots of others have gone into depth on this, and my take is "not well". Fanboys keep pointing to the 140,000 iPhone apps that will make it useful, but, um, laptops support pretty much every app ever written (i.e., millions). The iPad has a browser that's comparable to a desktop browser, but even netbooks have a desktop browser.
Yes, the UI is wonderful (it really is), but not wonderful enough to compensate for all the other shortcomings (no support for desktop apps, poor connectivity options, tiny storage, un-interchangeable battery, etc.). I also believe that people will ultimately prefer a mouse. It's not as sexy, but it's faster because it takes less effort to move a mouse around a 2" square surface than to move your whole finger/hand/arm across a 9.5" area, and everyone is already used to using a mouse. Touch is more intuitive, but a mouse is faster.The Newton wasn't pocketable either...