I use Automator to scale images down nice and quick (via an application droplet in the Dock). However, I very often use layered files, and it seems Automator is not a fan of Photoshop's layered PSD files.

Well, if you want to use automater to scale down, convert to JPEG, and do more to your layered files, save them as layered TIFF files instead. Layered TIFFs can also have some pretty nice compression (LZW or JPG), should you need to send layers about. Zipping up the TIFF always shaves a few more MBS off, too.

[robg adds: This seems to be an issue, at least based on my testing. A layered PSD file seems to work -- Automator puts a green check next to each step in the workflow -- but nothing is changed in the Finder at the end of the workflow. Using the same file as a layered TIFF, though, made everything work as expected.]