I think people miss the point that people that couldn't afford the book in the first place, or are unwilling to pay for it, could just as easily get it for free at the local public library.
People willing to buy books will continue to buy books and support the authors.
Those that wouldn't buy it in the first place most likely never will so nothing is actually lost to those people except they now possess something that doesn't rightfully belong to them.
Of course there are people that read entire books sitting in B&N or Borders that never buy them either, what can you do?
IMO a good preemptive strike used by some eBook publishers is to give away the first chapter free so you can try before you buy, which is the main motivating factor IMO, to see if you like the book in the first place.