In my first attempt, the epub-version of book Into Programming did not open in iBooks on the iPad.
After some debugging i found the problem, and it is now fixed. It turned out that I had an extra blank line in the mimetype file, and that caused the problem.
It was a little bit tricky since the book opened fine in other readers, and it was also considered Ok when I did validation in Sigil.
Links to the book, in its different formats, are now collected on this blog’s Books page.