Apple is releasing their tablet PC today. According to NPR, they plan to include an e-reader. As I mentioned in a previous post, I though that the tablet was the perfect medium for e-books, and would supplant the Kindle, Nook and other current e-book devices. Only time will tell for sure.
The move by Apple is brilliant. It already has a first class distribution model with iTunes pushing out applications and music for the iPhone and iPod. e-Books are just a natural progression.
From an XML publishing standpoint, EPUB is a relatively easy format to render. The DocBook XSLT stylesheets has an EPUB format built in. I'm not aware of one for DITA yet, but I can't imagine that it would be too far behind, or difficult to build.