Just installed Cat-Pass and it works great. Posts in a category show up as titles, but when I click on them, I have to enter a password to view the post content. One password for everything, which is nice. The "unlock" button you click after entering the password is in German... but if you don't mind that, it's all fully functional.
I would LOVE to see something that allowed you to enter the password once and then access all the posts without re-entering the password (at least in that session, until you left the site or logged out).
Love this plugin... especially since it's the only one I've found that works and does what I want it to do!