Here's a screen capture from my iPhone: I touch "1.f5" on the left side (the text of the book), and the move is made on the board. And I can shuffle the pieces investigating my own variations (as long as the moves are legal). Cool.
Here's a screen capture from my iPad: as you can see, there's a lot more room on the larger screen.
Silman's Complete Endgame Course is available in this format for $17.99. You're much more likely to study the iPad version than the paperback! But unless you absolutely love your iPhone, I wouldn't buy the book to read on the tiny platform: just too darn small. But that's not the fault of this great app. There are even nuggets of Silman's wisdom sprinkled through the text as audio files. To be clear, e+Chess falls far short of the true multimedia available through ChessBase, but this is a promising start.
There's also a Valeri Beim book on middlegame strategy available in this format (Beim is one of my favorite authors, but I'm not familiar with this book), and a few oddball titles. It remains to be seen how popular this format becomes (e+Chess could go the way of Betamax). And the serious player is more likely to get more utility from ChessBase or PGN formats. But ease of consumption is a strong counterargument: the platform looks very promising to me!
If you own an iPad and you want to join Vince Hart in studying Silman's Complete Endgame Course (an excellent book for anyone from complete beginning to aspiring master), you can't go wrong downloading e+Chess. If you own an iPhone, download it anyway, if only to read a free interactive copy of Chess Fundamentals, one of the greatest chess books ever written. But I wouldn't spend money on content unless you're buying for the iPad.
White to play
As long as we're on this page, here's a famous passage. Capa writes, "In the above position White can't win by 1.f5. Black's best answer would be 1...g6, draws. (The student should work this out.)" Your thoughts, students?