Hi guys,
Saw the conversation about Joomla and wanted to add my 10 cents. First of all Joomla was the first CMS I started to really get involved with. However after some time I've come to see many flaws in the system.

The new 1.5 is a huge step forward but it still claws onto the old concepts of 1.0.XX which goes back to the Mambo way of thinking. I don't like the fact that you need a mambot (now plugin) a module and a component. I think it complicates the situation. Just call a plugin a plugin.

I've actually written up an article about Joomla.
Comparing Open Source Content Management Systems - Gavin Doolan

I plan to cover Drupal next and discuss how it works. You should really really look into Drupal it's improved much since version 4.7 and the latest release 6 is out now.

There is one other CMS that I have been really impressed with and that's Expression Engine - It's not open source but the templating system is amazing.

Baz have you checked out the tutorials on compassdesigns.net for Joomla? That might help with building a more semantic template.