As I noticed on Apple Website, the SDK for developing 3rd party applications for iPhone/Touch will be available in February. This solves the biggest problem - offline reading - because with SDK, storing a downloaded copy will be trivial. It also will most likely fix the annoying lack of updatability of calendar and add few more interesting apps.
It is only matter of time until the other eBook formats will be be readable on iPod - such as CHM or PalmDoc (non-DRM-ed version).
With only 8 days remaining to Leopard and this anouncement, it feels like Christmas is here early this year :-)