[Kumabjorn]

I own a Kindle, hence my frame of reference is limited to that platform.

Is there a lot of foreign language learning materials out there for E-readers? I can see how a Kindle DX in landscape mode with side-by-side display formatting, combined with the built-in audio formats would actually be close to the optimal language learning "book"
The keyboard enables you to enter answers to quizzes. Unless you answer a certain percentage correct, you won't be able to move on to the next level. If you answer certain questions, say grammar related, completely wrong, the book automatically returns you to the grammar section.
Side-by-side display will give you the text in your native language and in the foreign. Or you can run a conversation, with annotations on the side next to it.

I imagine that the iPad must be even more advanced, with video capabilities, than a Kindle. How is it on other platforms? Are there products, like I vainly tried to describe, available out there? Do they work? Has anyone tried learning a foreign language through an E-reader?