Apple just updated the AppleScript section of its site.
I have never found a practical way to use AppleScript in my workflows... Hopefully the new version and better integration between applications and OS will make that a no-brainer now...
I have more hopes for Automator, especially the new version that has full access to the user interface (see here).
Here is the state of the documentation about Automator on Apple's developer's site. It is not updated yet for Leopard but is a very good start (after the Help files themselves) for people who want to take a serious look at this technology.
It is also possible to create actions with AppleScript or other easy to learn languages.