For best results with iPad, use the Format bar to select fonts;
the Format bar’s font list includes only fonts that are available
on the iPad, so the book should look the same in iBooks Author and
in iBooks on the iPad. If you use the Fonts window to select your
fonts, all fonts available on your computer will be listed.
Selecting a font that is unavailable on the iPad may have
inconsistent results when you view the book in iBooks.
Regular books from the iBookstore support embedded custom fonts, so this is a little disappointing. Hopefully it’s just a didn’t-get-around-to-it-yet 1.0 limitation.