I just came across a question which didn't have any tags apart from untagged. I was a bit baffled by this and clicked the tag to find that there about ten questions with this tag (and no others).
However, this question by Lars is also untagged and has not been migrated which means that users can actively select it. The untagged tag is an oxymoron and its pure existence allows users to tag questions with it which makes even less sense.
I think we should get rid of this, in my opinion, absolutely nonsensical tag and replace it with a, e.g., migrated tag.