If you install the free alternate svox classic speech synthesis, and get the $2 grace american english voice, my wife says it sounds better than some of her audio books.
(We use svox grace for all our droidx speech applications. Why they don't just include that instead of the crap default voice tech is beyond me.)
That said, if you are reading sci-fi or fantasy, its probably going to mangle some place or people names, but that is kind of expected.
That was one of the big features I wanted moonreader for.. ebooks to audio books. Now if only moonreader supported pdfs. 8(