I’ve been asked how the technorati-like cloud to your right is achieved. Being something of a gadfly, I had already upgraded my WordPress install to use Widgets, which I believe all the cool kids are using nowadays. The instructions to install the basic widget setup are pretty good, so long as you actually follow them rather than doing half of them and then assuming you’re done (but who would do that?)
After that I found the Category Cloud Widget on the Widget Blog(widgr.com, anyone?). Installation was again straightforward, the only trick to keep in mind is that you have to activate the widget just like a plugin from within the WordPress admin pages.
Once installed the parameters to make it work are straightforward – I set it to scale from 70% to 250% of the standard font, which seemed best suited to this theme as it uses relative sizes rather than absolute values.
The widget code was taken from this normal plugin. This is probably a bit easier, but lacks your RDA of AJAX I’m afraid.