That is THE key observation about how big of a hit this thing might be. Long before iPod, much of the world longed for a small package way to carry around a lot of their favorite songs. Long before iPhone, much of the world wanted a better cell phone device that blended a few other devices in an elegant way into one package. You might say the markets for both of those launches were quite hot for them, and that timing was excellent for such a release. In both cases, Apple didn't have to create the market or the market need... just offer an excellent solution for a glaring market need.
What is the glaring market need to be fulfilled by this Tablet product?
Don't get me wrong, I too am in the in the market for a new portable computer right now (time to retire an old PowerBook). I strongly believe a MacBook Pro is going to be the thing to buy, but I can wait a few more weeks to see if this thing could somehow cover the same mix of needs good enough, that it might be preferable to a new laptop.
As I keep thinking it through, I keep picturing the same (new) content via iTunes being available on that MacBook (or even that Powerbook) too, so it doesn't seem like all these new e-magazine subscriptions would be locked into an exclusive via a Tablet. It seems plausible that it will be thinner and lighter than the MacBook, but how big of a deal is that if it trades off a lot of capabilities? It seems likely it will be a cheaper than a MacBook, but when you use such stuff for work, even a thousand dollar+ difference isn't that big of a deal spread over a few years (use) time. What could be the big hook?
And before someone says it is just another product to buy WITH that Macbook, I have a hard time picturing BOTH getting tucked into the travel bag. Tucking a small iPod in with a laptop is not a big deal. Tucking a 10" screen in with another bigger screen product seems like a lot of bulk and weight to carry around when perhaps either could cover the bases for any given trip.