Digital Books
Books in digital form are the wave of the future. What is less clear is just what the digital book will be like. The big players in the business are experimenting with various readers and protection schemes.
Special Readers
Microsoft, Sony and Adobe each have special readers using Digital Rights Management (DRM). http://www.eff.org/issues/drm
http://wiki.mobileread.com/wiki/E-book_Reader_Matrix
http://www.microsoft.com/Reader/default.mspx
http://en.wikipedia.org/wiki/Microsoft_Reader
http://en.wikipedia.org/wiki/Sony_Reader
For boaters the Adobe Reader has some issues that you should read about, here is the URL link.
http://en.wikipedia.org/wiki/Adobe_Acrobat
Encapsulated books using an .exe format will generate a warning when you attempt to load and run them since exe files contain executable code, which can contain viruses. One of the solutions is to digitally sign the exe file to authenticate the source of the original file and its author. Thawte sells digital signature service but it costs $300 a year for the author or publisher, so many small publishers can't justify the cost.
Digital Signatures. http://en.wikipedia.org/wiki/Digital_signature
Copyright issues and various permissions like the GNU licenses.
http://www.gnu.org/licenses/
see the Free Document License section.
Encapsulated books using an .exe format and an activation code or key. The codes generally look like xxxx-xxxx-xxxx-xxxx and use numbers and alpha characters in the key. Books that are encapsulated generally are based upon a PDF format, which may or may not have specific protections and limitations. For instance, certain options may be turned off like printing or the printing may be limited to low resolution. Copying and selecting of text may be prevented.
Some schemes require access to the Internet in order to obtain the activation key or to open the book for reading. These issues will impact boaters particularly where you don't have access to the Internet to activate keys or if required when opening an eBook.
By the way, these issues apply to any digital media including still pictures, video and music as the computer is brain dead and doesn't know a book from a video. It takes smart software to know the difference.