As a product, the iPad is not going after 'market share' as this is a whole new product maybe a whole new market even. But it will definitely eat in to the sales of netbooks, PCs laptops, even Macbooks, and iPod touches.
It just occured to me that it may well be a huge success in numbers for another reason. I'm not sure of the numbers, but Apple sells more iPhones and iPod touches than it sell any other computing device. And a very large percentage of these iPhone and iPod touch owners do not own a Mac laptop or desktop.
So, for these people who have a iPhone or iPod touch, but not a Mac, the Mac vs PC argument means little. Even the OS in their hand held device matters little. For such users - of which there are millions - who also own many AppStore apps, the iPad represents a device which...
1. runs all their existing iPhone/iPod touch apps.
2. allows them to surf the web on a larger screen anywhere.
3. allows them to see movies on a larger screen anywhere.
4. make documents, spreadsheets, presentations with a 'touch'.
5. may one day allow them to buy and comfortably read books on a hand held device.
6. play a variety of games on the go.
7. listen to all their music.
6. costs less than their iPhone (in many countries).
Now that sounds like an attractive device.
That's how it will appear to a large percentage the 75 million or so iPhone or iPod users especially outside the US in countries where the iPhone sold even for about US$ 700-900 and was still lapped up.