I'm using Tiny Tiny RSS v1.2.20 on FreeBSD with Apache 2.2.6, PHP 5.2.5 and PostgreSQL 8.2.5. I'm using SimplePie? as my feed parser.
I added a number of feeds to my primary account within TT-RSS, though didn't initially mark any of them as hidden. After I decided to also open it up to some friends of mine, I went back and marked three of the feeds beneath "My Feeds" with the "Hide from 'Other Feeds'" option. However, if I log in as one of my other users, I can still see those hidden feeds under the "Other Feeds" tab. I've not received new articles on any of those feeds, so I don't know if it marks them on a per-article basis or not.