Aperture allows you to set up Folder Naming presets but they are mostly limited to capture date/time, current date/time and the Project containing the images.

Aperture Assistant can export to sub-folders based on any metadata present in Aperture, for example making sub-folders based on the IPTC Country Name and the image Rating, or the camera model and ISO speed.

Setting up the Workflow

1. Use a Source Node to get the images.
2. Use a Text Node to grab metadata for each image, adding a '/' character for each level of sub-folder. This explanation of tokens has a specific example.
3. Use an Action Node to add Finder sub-folders based on the text passed through from the Text Node.
4. Add another Action Node to export the Versions, Previews, Thumbnails or Masters.

You can see an example in this screengrab, and download the sample workflow file.

When you run the workflow, new sub-folder will be made as needed depending on the metadata for each Version chosen.