Summary
Bottom line: If you're looking for a way to automate some basic tasks on your Mac fairly quickly and easily, Automator is your tool. For more complex workflows, AppleScript provides greater flexibility and reach (but requires more time and effort).
Ben Waldie, president of Automated Workflows, LLC, is the author of Automator for Mac OS X 10.5 Leopard: Visual QuickStart Guide and the host of the Mac Automation Made Simple video podcast series. For more of Ben's Automator and AppleScript tips and articles, visit the Automated Workflows, LLC website, where you'll also find Ben's third-party Automator actions for InDesign, Quark, Photoshop, and more, as well as information about custom AppleScript and Automator development.