So basically Cesare's thing is that if you purchase the ebook and genuinely don't like it, he'll give you the option of either returning the book for a refund (which he'll send to you snail mail) or swapping it out for another one of his works. The offer is good until the end of August, but I believe that this only applies to Amazon purchases.
I've spoken with Cesare and he said that he's willing to honor requests from any merchant site, as long as you have your receipt. I'm expecting that few, if any, will actually take him up on this though. I've also posted a link to Cesare's blog entry that gives further details on the offer itself.