Originally Posted by DaleDe
While fixed layout ePub is part of the ePub 3 specification it was only added after the fact that many publishers had already developed their own systems which were really extensions to ePub 2. At this point there has not be agreement on the fixed layout and you will likely need a different one for each device. For reference see our wiki Fixed layout ePub
Unfortunately it is a little worse than what Dale said, but we are working on it.
I'll be a bit a spec geek here - the current FXL document for EPUB3 is an informational document, and while it is intended for inclusion in a spec update is not part of the spec yet. We (the IDPF FXL ad hoc group) are working on updating the document (adding new features), prior to it's inclusion in the spec.
In addition there has been a seperate working group formed: Advanced Hybrid/Layouts
, that is looking at how to formalize some of the interesting things that can be done with multiple renditions (think portrait vs landscape, or fixed vs flowable).
Hopefully things will get a little easier for the content authors/publishers after we finish.