If you move a skin from Windows to Mac, be sure you set the permissions on the files. All of my files were set to 600. Products showed in the Zope product list, but not in Plone's. There were no errors in the log.

To see if Zope was really reading the products, I removed the .pyc files, then restarted Zope. The .pyc files weren't being created. Changing the permissions to 644 did the trick.