f a user logged in then favorites data will saved in database instead of cookies.
If user not logged in data will saved in cookies.
You can choose "only registered users can favorite a post" option, if you want. Also there is a widget named "Most Favorited Posts". And you can use this template tag for listing most favorited posts;
Most Favorited Posts
If you use WP Super Cache you must add page (which you show favorites) URI to "Accepted Filenames & Rejected URIs".
If you need support create a topic on support forum
