I just came across a real gem for Joomla. Dwight Jack has posted a way to upgrade your Joomla 1.5 site to use the latest Mootools version, instead of Joomla's lame duck Mootools 1.11. He's done this without the need to hack Joomla's core files, and has also posted an updated version of the Mootools compatibility script.
I can't wait to try it for myself!
As of version 1.5.19 onwards, Joomla now comes with its own Mootools Upgrade system plugin. Therefore the above method is now no longer required! All our products (ParaInvite, SIMGallery, and SIMAnswers) will now work out of the box with the Mootools Upgrade plugin enabled.