Apple says they've sold a million units a month for the first two months. I wish all those folks were hot to read books on their iPads, but I suspect that, for most iPad owners, reading ebooks is a secondary or even a tertiary activity, after web browsing/emailing and watching videos. But even if only a quarter of them read even one ebook, a quarter of two million is half a million. That's a lot of new ebook readers, and that, I think is what is going to help drive the push to digital publishing, especially if sales continue at anything like that rate. Whether or not the publishing industry is ready for that push is another question. The answer seems to depend on whom you ask.
Whether publishers are ready or not, I'm hoping iPad owners share a key trait with Kindle owners. Once they have a more convenient way to read, they buy and read more books. I am all for that!