It would be interesting if you could ignore/mute based on user AND tag.
Thus if you had followed User because you noticed they posted a bunch of really great stuff to #foo and then found out they posted a lot of really not great stuff to #bar, you could ignore User&#bar. Or whitelist User&#foo if that's all you wanted to see from them.
Presumably tags also work on an OR basis, so if you're subscribed to #foo you would see a post tagged #bar AND #foo, even though you never, never, wanted to see anything tagged #bar. Which may be non-ideal for some use cases (e.g. #nsfw).