AppleScript has long allowed users to combine the abilities of multiple applications in new and unexpected ways. Automator takes AppleScript's application integration technologies a huge step further. With Automator, end-users can drag-and-drop actions from various applications into a single, saveable workflow. It's similar to writing shell scripts and piping the output of one command-line tool to another with pipes, but with a visual interface.
Tiger's themes seem to be search (Spotlight), metadata (Spotlight database) and end-user extensibility (Automator and Dashboard).
I'm persuaded Tiger should deliver real value to me. I doubt it will work well on my G3 iBook of course, so the real cost is much higher than a $130 upgrade price. It should work well on the new G5 iMacs.