jim said:
>   I want to read ePub or Mobi on a decent ebook reader
>   which will allow me to set things like font sizes and margins.

try ibisreader.

>   http://ibisreader.com

you can try it on your desktop machine to see if you like it.
and it's on the ipad.  plus it is under _active_ development.

i don't know if "eucalyptus" is ipad-native yet, but when it is,
i would definitely recommend that as a worthwhile viewer-app.
(it has shortcomings, but from a reading perspective, it's fine.)

-bowerbird