We have a lot of direct mail that need vanity urls. This required constant management of these urls almost every week.  We needed to make them case-insensitive due to our audience and some direct mail that somehow got out the door with capitals.  We started going down the route of regex “^/(?i)” in front of url to make case-insensitive.  The caused a problem because I was wanting power users to be able to manage these redirects in the future through a plugin.  I also called our hosting company WPEngine to add the apache/nginx module to make on server side have case-insensitive but because of their standard builds they were not able to implement.  So that lead me to find this article that created a plugin that looked for caps and made lower on the init of WordPress.  Here is the code below and also link to the source.
http://code.rawlinson.us/2012/01/force-wordpress-to-be-case-insensitive.html

<?php

  /*
  Plugin Name: case-insensitive-url
  Plugin URI: http://www.unfocus.com/projects/
  Description: A plugin to make wordpress case insensitive in regards to urls.
  Version: 1.0a
  Author: Kevin Newman
  Author URI: http://www.unfocus.com/projects/
  */

  function case_insensitive_url() {

   if (preg_match('/[A-Z]/', $_SERVER['REQUEST_URI'])) {

    $_SERVER['REQUEST_URI'] = strtolower($_SERVER['REQUEST_URI']);

    $_SERVER['PATH_INFO']   = strtolower($_SERVER['PATH_INFO']);

   }

  }

  add_action('init', 'case_insensitive_url');

 ?>