What will determine if the iPad is sucessful will be whether or not it has a killer app that will get people to buy one. I see some real advantages to a bigger screen "iPhone" for some applications, but I think eBook reader or web browser is not enough. iPhone is great cause its a phone, iPod and a very easy to use portable gaming device with graphic capabilities to give a DS and PSP a run for their money.
iPad too big for a phone, too expensive just to read eBooks (something I won't do cause I don't want to lease books) and underpowered compared to a netbook.
So I'll wait and see if there comes a killer app that makes me won't one. Right now, no.