[eluser]slowgary[/eluser]
Each include is another HTTP request. So Xwero's approach would be ideal, rolling them into one. I worked with a company whose CMS was made to roll all the CSS files into one and name is a hash of all the files, that way every time you change which files you're combining, the name changes too. It saves your browser from caching new CSS.
My opinion is that you'd be better off combining everything and having the client download code they might not need, then to have them download 15 different files. They might have to download code they don't need, but your JS can be minified and it will likely be faster for the user having less requests and little higher filesize. Not to mention, all the CSS & JavaScript for your site will now be cached, so the user will already have what they need for new pages - sort of like prefetching.
