Just perusing through cake's webroot, I noticed a PHP file in the js directory called vendors.php. It seems its idea is to allow you to keep a global repository of javascript files in cake's main vendors directory. This is a great idea for those of us who develop multiple apps with one cake install. So I had a little think and realised I could do the same thing with my CSS files and images. So I set to work modifying this vendors.php file. So now if I want to include a link to a global javascript file located in cake's vendors directory, I simply do this in my view:

$javascript->link('vendors/myjs');

Adding vendors/ before the filename simply tells the javascript helper that it should look in the global vendors directory for the file. Of course it works normally if vendors/ is not prepended and includes files from your webroot. I can do the same thing with CSS:

$html->css('vendors/mycss');

So how did I do this?

Simply edit the vendors.php file in your webroot/js directory (or create it if it doesn't exist) and add the following code:

/**
 * This file includes js vendor-files from /vendor/ directory if they need to
 * be accessible to the public.
 */
$file = $_GET['file'];
if(is_file('../../../../vendors/js/'.$file))
{
    readfile('../../../../vendors/js/'.$file);
}
else
{
    header('HTTP/1.1 404 Not Found');
}

Now you just need to create an .htaccess file in your webroot/js directory with the following content:

<ifmodule>
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^vendors/(.*)$ vendors.php?file=$1 [QSA,L]
</ifmodule>

This is required, so this whole thing will obviously only work if you have apache's mod_rewrite enabled. Now just create a directory called js in your global vendors directory and place your javascript files into it. Now you can include your javascript files from a central repository shared by all your apps. Just rinse and repeat for your CSS and images directories. Not forgetting to edit the file paths, etc.