Question Mootools; selective enabling

Well, the [Mootools] filename may be referenced on every page (and the references may not actually be invoked) but the file is not downloaded every time someone looks at a different page on your website. As you know, files are stored in your browser cache and they're only downloaded if your cache is cleared, if you force a page refresh or if the cached version of the files are different to the version on the server. Therefore, page load times should be insignificantly affected.

Do you have empirical evidence of the differences in the page load times between running with Mootools loaded and not running with it?

As I may have mentioned elsewhere (I can't remember the specifics), Joomla 1.6 will include the ability to selectively use extensions in different parts. I don't know if it helps knowing that. :S

Yes I know that, its just that most visitors wont use the forum and it doesnt make sense to require a 75kb additional weight to visit my website (which is entirely designed around the idea to be fast to load, or at least for joomla standards fast..).

I really appreciate all the help I got, and hope that I understood correctly that it should be possible to load mootools only on the forum pages or only for logged in users (also for Joomla 1.5)? Or is it simply no possible; in that case I have to weigh the pros and cons of 1.6 vs 1.5 (but it would be terrrrific if I could just learn a way to have mootools only for kunena parts )

I got one step closer (I think) as I was recommended to disable mootools, and insert this code into my template:

<?php
$user = JFactory::getUser();
if( !$user->guest ) : ?>
<script type="text/javascript" src="/media/system/js/mootools.js"></script>
<?php endif; ?>

This way mootools is loaded only for logged in users. The strange thing is that although when I look in the source when logged in, mootools.js is listed, but the BB code doesnt work.

Hope someone can help me out, I would really like to understand how to do it!