Touchscreen eBook for Math

I believe that a touchscreen eBook for Mathematics would be of great benefit to Mathematics education, and a great tool for mathematics students.  I can think of several advantages.  This could all also apply to physics books and other texts, although some more than others.

• Size/weight - ability to store multiple books.
  
• In the actual text, figures, example problems, and other on-screen clutter can be minimized and only shown when the students selects it to be shown to reduce visual distractions.
• Since figures would be more efficiently stored using programming code and parameters as opposed to storing them as images, it would be easy to make each figure interactive, allowing the student to see the effect that changing different parameters has on the figure.
• Since example problems start as minimized, it would allow the student to try and work the problem on their own, and if they get stuck, slowly reveal the solution, and allow them to check their procedure AND answer.
• The student would be allowed to write minimizable notes in the 'margins' of the book, allowing them to summarize the text w/o the fear of visual clutter or of damaging the book.  
• Homework could be done in the book itself.  Imagine this scenario:  A student goes to do the homework, selects the problem they are to do and the problem moves to the top of the page, becoming the sole element on the page other than the student's work area.  Then, the student can make the solution area smaller to allow them to browse the text if they need help solving the problem.  Furthermore, graphing and other solution utilities can be available to the student, removing the need for a separate calculator.  
• Homework could be transmitted wirelessly to the teacher and the final answers could be checked automatically by the teacher's 'reader', allowing the teacher to focus on checking the solution process.  Furthermore, the teacher's 'reader' could easily provide statistics regarding the class' work (mean, median, mode, standard deviation, histogram of scores, etc) and serve as a grade book.
• Updates and corrections to book material can be made easily.
  

There are however problems with the idea.  It seems to me that if this product actually came from a textbook publisher, it would be terrible, restrictive, and have depressing licensing issues.  Also:

• Reader would have to cost something, and there is often no explicit cost to young students w/ traditional textbooks.
  
• Batteries suck, but should be manageable
• Licensing of book material - permanent? temporary?  Should students license it, or should schools license it and rent it to the students?
  

All in all though, I think that the idea is amazing and is definitely worth pursuing.