Just so you guys are aware; there is no option to ban users any longer. Agoracom felt the ingnore feature (installed fairly recently) served the same purpose and allowed individuals to make the decision for themselves. So although it may be annoying to see responses to posts started by ignored users its just about the only option if you're frustrated.

Besides, banning a person is good in theory but there is nothing in place to keep the banned users from coming back under a different alias.

FYI - If you do in fact want to ignore someone simply click on their name and select the red "ignore user" button on the left hand side. The same button also appears near the right of their name when you click on a post they've made. In both cases the ignore button is right near the 5 stars you use to vote on a person.

Hope that helps.
Cheers.
Gamblor.