Is there there be a way to filter a user and hide it from discussion without downvoting? Or even filter a topic from the main stream? Since there isn't would this be a feature that people would want?
Although there is no built in functionality, there is a greasemonkey script available (thanks to Ben Brocka for pointing it out):
It is not encouraged that we use this script. If we all ignore a problem it will only escalate. However, given the constant activity and lack of improvement of some problem users I can see why you would want to use it; I am extremely tempted myself.
I have not tried running the script, but will report back with any success or failures.
I do not think that the website provides the functionality of hiding questions or answers posted by certain users.
To hide questions with certain tags, specify those tags as “ignored tags” and check the “hide ignored tags” option in the “prefs” page of your profile. See Hide questions with a specific tag.