The National Genealogical Society, ever proud of its third printing of Thomas W. Jones' tour de force Mastering Genealogical Proof, has announced that the book is now available in digital format for the Kindle ($9.99). They are also working on a soon-t0-be-announced Mac iBooks version.
Currently, one may order the paper edition at the NGS website for $30 (nonmembers) or $25 (members). I already have my hard copy, purchased at the NGS conference this past spring. But, I'd love to be able to have it on my iPad.
One thing I'd not noted before is that the NGS website now has ten corrected pages for the book. These would be great printed and tucked into one's hard copy or saved as a file along with the digital version.