I applaud your DRM-Free, multiple format publication of ebooks. I prefer to conserve resource by downloading instructional books and I like taking my reference books with me when I am working at a client's place or traveling.

However, I heartily concur about the upgrade issue. I just bought a Kindle and can't afford to upgrade all my Wrox books to mobi/kindle formats at 35% off the printed copy list price. I like to have print copies of reference books because they are easier to use when working at my desk while the Kindle is easier to toss in my attache case.

Apress upgrades for $10 after answering a question about the book and O'Reilly upgrades for $4.99. Please find a way to make this happen.