E-Reader Courtesies

So I'm sitting on an airplane yesterday, flying to Chicago (hello, Chicago!), and the man sitting next to me (and too close to me, if you want my opinion) pulls out an iPad and opens his Kindle reader. The angle at which he holds the device allows me to see that he is reading Matterhorn, a book I've had my eye on for some time.

Now, if this were a print book, I would not have hesitated to make a bit of small talk and ask about the book. But if this had been a print book, I would have recognized the book by its cover, not by looking over the man's shoulder (I guess I'm nosy like that). And I would have been able to see how far into the book he was - if only five pages, I wouldn't ask how it he liked the book, you know?

In the spirit of not being that obnoxious person that talks too much on an airplane and snoops into others' business, I let the matter go. But it left me thinking: what is acceptable in this (or similar) situations? Is it ok to admit that I can see your iPad screen perfectly clearly and am interested in what you are reading? Is it rude to peek in the first place?