Set a unique upload path for each site on a multisite network (MU Plugin)

multisite-upload-path.php

<?php
add_filter('upload_dir', 'mu_media_upload_dir');
function mu_media_upload_dir($upload) {
	$site_title=str_replace( ' ' , '_' , get_bloginfo('name','raw') );
	$upload['path'] = ABSPATH . '/shared/' . $site_title;
	switch_to_blog(1);
	$upload['url'] = site_url() . '/shared/' . $site_title;
	restore_current_blog();
	$upload['subdir'] = "";
	$upload['basedir'] = $upload['path'];
	$upload['baseurl'] = $upload['url'];
	return $upload;
}

This is an MU Plugin that automatically saves media uploads to /shared/<your site's name>
It replaces spaces in the name with an underscore