I love a good tagging system, if it is done properly. It makes it so effortless to find the content you want. I broadly like this post, but I disagree with "Th

I love a good tagging system, if it is done properly. It makes it so effortless to find the content you want. I broadly like this post, but I disagree with "The lesson: don’t let users encode logical paradoxes.". If a user says they want (A && !A), just hand them back nothing. Let the expressiveness exist regardless. (Ideally, warn the user, though) I want expressive tags. It makes everything so much easier. If I can't do (A && B) || !(C or D) then as a user I'm going to get frustrated if there's a lot of content to sift through. Grouping and negation are critical, IMO. The post touches on this, but I'd say by far the largest issue is the moderation of tags. If only the author is allowed to tag, and there's no moderation or oversight from other users or official moderators, the tag system is effectively useless. Some users will be lazy and not tag effectively. Others will tag incorrectly by mistake or intention. You want the system to support new tags for a variety of reasons, but this allows typos to create new tags. Generally, when I see that a tag system sucks, it's because it's been mis-used, not because the underlying logic is bad.