Yes, epub is relatively new and there's still some extra-work to do for both content and software/hardware support.
I've been playing with the format these last few weeks and I must say that what we're generating with our latest test on Feedbooks is much nicer than OEB already. TOCs are a bit too complicated to generate though, and I was wondering about 2 things:
- hyphenation: Are soft hyphens supported ? Will some of the software supporting epub use an auto hyphenation ?
- Is there any online ressource to check if an epub file is considered valid or not ?