Bah, this highlights several large problems, imo. First DRM on everything. They got the DRM out of music, why is it still on everything else? People who are paying $300-800 dollars (various eReaders, iPad, etc) for a device which they want to use to read books on shouldn't be subject to this sort of whim. Amazon and a publisher can't get along and *poof* Kindle readers can't buy those books anymore. I don't care if Amazon doesn't want to sell their titles anymore, but you should have the option to go buy the book elsewhere and use it on your eReader. This goes for Apple and the iBook store as well. If they are using DRM (sure they will be) I won't be buying from them. (And if I cant sync eBooks from other sources onto the device I won't use it as an eBook ready, and it will lower my likelihood of buying one).
The second big issue I see here is the fragmenting of the publishing market. If we end up with half of the publishers o in the Kindle store and half of them on the iBook store, we all lose. No good can come of this.
Lastly is the failure of old media to adapt to the digital world. Again. A new hardcover book runs $25-30 cove price. Most are discounted to $15-20 from their release day up through the <$10 paperback edition. $10 for an eBook copy seems pretty reasonable when you figure there's no printing cost, no shipping from printer to seller, and the consumer loses the ability to resell the book (so a person who would have bought a used copy and netted the publisher $0 would end up with a $10, all profit digital copy). Personally, I think both Macmillan and Amazon are stupid. Macmillian for thinking they should charge more than $10 and Amazon for trying to stop them - I believe that the market would sort the pricing out eventually (of course the DRM factor would likely push prices about their natural floor).
Really hoping that I can just drop a text, PDF, RTF, or HTML file into iTunes and either convert or just sync it to the iPad for use in iBooks... this would actually really increase the amount I get to read. Unfortunately, the fact that it doesn't appear to be a built in feature, but rather an app makes me feel like I won't be able to do this.