I have noticed that a lot of great novel phenomena's start with books that are fairly small, before each next installation gets a bit bigger as the author/book is established. For example Harry Potter. Do you think the first Harry Potter book would have been as successful if it was the size of the last one (600 pages compared to something like 220 pages for the first one.) As the HP books became more successful, the page counts of each novel at each interval of HP-mania went up. However Twilight seems to have dived in straight at the deep end and Stephenie Meyer who had never written a book before in her life got her 500-odd paged Twilight published no problem, prior to the fame of the author or success of the book. And that's considering that the book is a teenage/YA book. So how much of a big deal is book size if you're trying to get your first novel published? would a 500-600 page book be near impossible (even if it's a good book) due to commercial reasons?