Sorry guys, but I'm going to have to call you all out and say that luigimaster is actually onto something on this one. I too have noticed that these don't appear in my add-ons list, and have found that they've been incorrectly packaged. As the essential files have been packaged behind a folder within the existing zip file, instead of being put directly into the original zip file.
You can fix this by repackaging the zip file and removing the folder. But I hope for Kaje to quickly remedy this and make an 'official' fix himself.