I'm a professor too, and I know about those citation formats. Some of them are for online e-books, which can be easily checked or searched with a browser. You usually use this when you have no other choice.
You can't browse an iPad or kindle version in the same way, where the page number can vary not only according to the zoom level but also according to the chosen portrait/landscape orientation(which is an absurd).
My biggest gripe is again the lack of consistent page numbers. You can't distribute reading assignments easily, when some have printed books, some Kindles and other iPads. Once I had to take home a kindle from this graduate student so that I could check his interpretation over multiple passages. Didn't like the experience. How many readers I''ll have to take home next time?
The solution I pointed above would be easier: just indicate where there's a page break in the text, no matter zoom level or device orientation. You could have "fake" page numbers in the bottom, but on the sides, we would have the "original" page number for the edition where the e-book was based upon.
I'm not saying you can't use e-books, but use common sense. Don't use it for graduate level assignments, or any work where you think you'll be citing A LOT from. Don't use it when you disagree with the canonical interpretation of that work. Casual references are fine, sometimes you're just showing off your research anyway.
Stick to the canonical interpretation, and avoid citing controversial passages - of course people will think: "did the author REALLY said this? huh. Interesting, who knew? Where was that again? Let me check my copy. Oh, I can't, I don't have the exact page..." IMHO, it won't make you look serious, even if you follow all the above guidelines.
But thanks for posting all this, I'm sure it will help a lot.