If you answer a question, then do we have ethics regarding adding tags to it after the fact, or is that considered a form of "reputation boosting"? I just noticed I was doing this today, and realized that it could be used in a nefarious way by someone wanting to transfer reputation points from a large topic to a small topic.
Also, what about removing tags, so that you can cram more information content into the existing 5 tags (e.g. getting rid of threading, and replace it with java-threading)? I do this from time to time to other people's questions, but I am not sure whether it is right or wrong.