Categories are crucial, it shouldn't be that hard to create a dozen or so standard categories for users to tag their stories with. If this "Books for Mobile Devices" site grows like we hope it will, people aren't going to want to waste time scrolling though romance stories to get to sci-fi for instance.
A few more questions. Why LaTeX? If this is for books and stories and not academic papers why is it needed? (I know a bit about it but not that much). Also will users be able to download entire books, not just chapter by chapter. That's what I'm most aperhensive about, these files are custom and chances are many of them will be unique to your site. How do you archive them in a non-propriority format? If the software you're using to save them is no longer upgraded what happens to the files? I've just had several problems with my companies website in the past, they posted articles to the site that went into the database. When we wanted to upgrade the site, it turns out we couldn't export those articles and the software was no longer supported. (Copying and pasting hundreds of articles is not fun
)
BTW: are you designing this site from scratch or using a database program? If so which one?