A number of books are available in e-book (Kindle) format from Amazon.  The often-reduced price of some of these books is an attractive alternative to a paperback, and many paperback books do not hold up to re-use as the bindings do not lie flat and pages separate.

I own an ordinary Kindle and thought about buying an occasional book in electronic format, but my concern is for formatting (diagrams, etc.) on the small screen.  Does anyone have any experience in general with electronic copies of chess books?  Obviously purchase of a tablet would cost a lot of books.  Is a tablet a "necessity" for reading e-books or would a regular (not a Fire) Kindle work?

Everyman publishes a large number of chess ebooks in pgn format as well as cbv. Most chess applications handle pgn. I recommend the free software chessx which works very well with everyman pgn files.

Thanks @JamesCoons.  My concern was more for the on-screen formatting of positions and boards rather than a supplementary PGN/CBV file.  Of course, if PGN or CBV files are available, I can handle them with Fritz which is my preferred method of reading chess literature - physical book on my lap and the game on the screen.

I guess a related question might be if it is customary to have PGN or CBV files available with the book.  My older chess books have been PGN'd and placed online (games and positions only, not text) which is handy.  But new books in Kindle format (Amazon) seldom if ever state if PGN files of the games are included.

With almost all of the Kindle books you can download a sample for free, which you can read on your device, and you can return any Kindle book within 7 days. 

So I would start with downloading the sample, and then deciding if you want to buy a certain book.  If the sample isn't large enough to tell, then purchase the book, and if the diagrams don't look good, return it. Every book seems to vary in the quality of the diagrams.