iPad and engineering textbooks

I have read opinions that the iPad could be attractive to students because e-textbooks would be cheaper and lighter to carry compared to physical textbooks.

I have some other benefits in mind.

Today, I have been doing some Mechanics revision. An iPad textbook with moving diagrams and interactive content would be immensely valuable for my studies.

I can think of so many benefits of electronic content systems that Engineering textbooks could make use of. Here are just a few ideas:

Lots of these things are available now. PDFs can have collapsible hierarchies to navigate content. There are interactive Java applets scattered about the web.

What I am looking for is the comprehensive quality of textbooks combined with the benefits of the iPad.

(I think it is already agreed that laptops and iPhones are not suitable replacements for books, but an iPad could be.)