Originally Posted by HarryT
Very true. MobiPocket is as close to a de facto standard as we have at the moment. That might change with Adobe's "Digital Editions" in the future, but for now, MobiPocket certainly gives you the widest choice, both of books and platforms to read on.
The book formatting part should be the same for Mobipocket and Digital Editions in the near future (it's normal for Mobipocket to updgrade from OEB to OPS). The only difference should be on the DRM part of the file.