I think the best way to do this is a "include page" type of capability, which would allow embedding one page in another. This keeps things simple – tags, permissions, etc. all stay the same. Plus, this would allow a given section to be embedded on multiple pages – useful in a variety of cases, especially navigation.

Ah, now I see this post! I just created my own similar suggestion. Mine was to be able to add tags to blocks or groups within a page. Then it would simply use permissions of groups to view that block. The permissions system already allows to view/edit/etc based on tags. Though this would complicated editing if you could edit the page but not the sub-group... Hmmm...

If I understand Sebvita's request, it is for sections of the page to be hidden, unless you are in the correct group. If this is the request, I need this functionality as well. Alternatively, the ability to embed a page, as a section of another page would also solve this for my team wiki.