Valloric--I would agree that based on my experience changing the default fonts would be preferable over embedding fonts. In my very informal tests, it takes about 3 secs for the page to change in the book with embedded fonts compared to 1/2 sec in the book with the default fonts.
For me, since I don't need any special font sets and I don't mind the reader's default fonts, I think that's what I'll stay with.
dordale