Jane wrote an excellent article on it at Dear Author at http://dearauthor.com/wordpress/2009/06/02/effectively-combatting-piracy/
I'd like to add that authors may (rightfully) rail and chide and scold readers for downloading pirated books, but the best way to get anything done is by pushing the big players in the industry to do something. As we have seen, pirate sites will always be around and there are always people who will want free stuff.
The thing here is that authors must accept is that readers can be selfish and put their own needs above the authors'. In this case, while readers may understand that an author needs royalties to survive, there will also be readers out there who find books too expensive and therefore, if piracy is an available mean to get the books they want, they will resort to that. You can scream and wail and call them pirates and scum, but that's how people can be sometimes.
Instead of sounding off on readers, maybe it's time to dogpile the industry players instead? For example, $9.99 is way too high for ebooks. Even if I have a Kindle, I'm not buying their books if they cost $9.99 each. I don't care if publishers whine that their ebooks are supercool and that DRM is an added value for money or whatever else they can tell me - I am not spending $9.99 on any ebook, period. And if you tell me this is the amount of money I must pay for ebooks so that my favorite authors can eat, I'd remind you that I have to eat too.
And then there is the matter of availability. As long as ebooks by these bigwig publishers are restricted to US folks only, I don't know why these people are complaining when people outside US resort to piracy to get their hands on those ebooks. My favorite move was by Wizards of the Coast who banned online retailers from selling legal PDFs of their out-of-print books to "combat" rampant piracy. Great move there - trying to beat piracy by making pirated copies the only kind of PDFs available to readers!
Anyway, my point is, arguing about morality is not the best way to combat piracy. Human nature being what it is, people are more likely to react favorably if you give them incentives to buy an ebook legally as opposed to getting pirated copies. Reduce the price, greatly increase the availability, and make it very convenient to buy a legal copy, like Jane said. And for goodness sake, authors should stop screaming at people and calling them scumbags because that is not going to get them to listen to you. When the RIAA started suing kids for downloading music, that was a PR nightmare because it made the RIAA looked like utter morons even if you argue that they were in the right to go after those kids. Unless the bigwigs in publishing actually do something, I suspect that the poor authors will have to live with the situation until someone pulls an iTunes for ebooks.
Push the industry players to do something. Railing at readers isn't going to change anything.