What would be useful is a category that contains hidden discussions, however the contents should be accessible by Search and displayed only if linked to from search results.
The reason is that I have a number of technical and help articles that are really dull and boring reading unless you really want the information contained in them.
So for example, an article on CMYK Colour Profiles lives in a discussion in a hidden category with keywords: colour, profiles...
A regular visitor to the site sees nothing unless they search for one of the key words, the article shows up in the search results and a simple click takes you to it.
Also, I have articles that I only want viewed by people I approve, so if I want you to view a particular article I will put 12345 in its key words and ask you to do a search for 12345.
Up until your last paragraph, wouldnt it be just as easily achieved putting all those articles into a single catagory then using a global preference to hide that catagory for everyone?
Nope. Search only finds what you have permissions to view.
This might be what you want: Hiding categories and still keeping posting privelages # 8, but there are still some missing parts--the category will still show on the categories page, and its possible to navigate to this secret category directly either by guessing the category IDs in the url, or following the category link at the top of the discussion.
Sorry, when I said hidden I meant blocked - therefore they wouldnt appear in users standard discussion listings (unless users chose to let them, ofcourse) however they would appear in search results. I assume ofcourse you have no problems with users browsing the catagory anyway (if it's a list of documentation it may be a useful ability, and some users may just enjoy being bored!)