I haven’t tested this plugin myself, but considering it’s at 1.6, it seems the development is quite strong, and should produce exactly what it claims. Basically it’s a plugin that allows for the seperation of the users from “members”, and then restricts the blogs content to only those registered members, including feeds. Which in essesence could transform your WP blog into a paid subscription service. I’d be interested to see some examples of sites using the plugin.