This 4.0 collection currently only supports CS4 and has a number of bug fixes, and 6 new actions.
Like previous versions of the Action Pack, this collection of Automator Actions lets you drive Photoshop from Apple’s Automator. These are not actions that you can run from within Photoshop’s Actions palette. This is a Mac-only product that allows you to build automated workflows that can go beyond what Photoshop’s built-in actions provide.
Ben is looking for feedback (bugs, etc.) on the new version. For more info on what the Action Pack does, see his earlier post.