In summary, when I export a book from InDesign to EPUB 2.0.1, it's displaying perfectly in ADE and iBooks on iPad. When I export to EPUB 3, the font is not displaying, and it's reverting to a generic serif in both formats. Typekit support has looked at my file and generated an EPUB 3 which is displaying fine for me in iBooks but not in Digital Editions.
I have "Include Embeddable Fonts" checked.
Typekit can't replicate the problem so I'm coming here to see if anyone else has had this problem.