As for Suster's suggestions, the first one would be a mistake. There are many situations when a throw away account is warranted, such as asking for anonymous advice on a tricky work situation, or submitting a controversial article.
For the second suggestion, it already exits. Once a user reaches a certain karma level s/he has the ability to down-vote comments.
For the last, an RSS feed on a user's "threads" page would likely be useful to those who wanted to be notified on updated conversations they are participating in.