Guys and gals, please try to keep this thread civil -- i see some people arguing with each other needlessly. Everyone is making good points, there is no need to get personal.
At this stage, a variety of ideas about different features of a tagging system is welcome.
As has been noted, I have reasons that i think an internal tagging system would be useful, and have wanted to put in such a system for quite some time. Mostly this would be a more general system to help in the creating the blog, newsletters, and year end reviews. The blog system I wrote is a kind of specialized restricted tagging system, and i think a more robust tagging system would be useful.
Being able to tag threads/posts for content and let people browse the forum using a tag cloud or by content could be very useful if we could get help tagging things, either by authors, moderators, or readers.
In my opinion, the NSFW tag is the *least* compelling reason to implement a tag system, at least for our forum (for others it could be very useful), but having said that, if we go to the trouble of writing a tagging system, adding the NSFW would be trivial, and offering the general ability for people to filter out threads based on their tag would be useful. Some people could filter out NSFW threads, others might filter out programming-specific threads.
So at this point we are in the stage of brainstorming, so feel free to let your ideas flow. Do keep in mind as has been suggested by others that eventually we will have to balance the work required to code this with the benefits, and figure out if it is something (the tagging) that can be done fairly painlessly and without adding much to the workload in terms of every day tagging.