A feature to ignore users has been added for users level 31 and higher. To use the feature, simply click on Message Detail for the user in question and you will find a button called Ignore User which will add the user to your ignore list. You will not see any posts or topics by any user on your ignore user list. If you want to remove a user from your ignore list, you can do so using the link found right above the button on the Message Detail page. As of now this is the only location to access your ignore user list but in the future it will be accessible more easily.
Keep in mind that this is a beta feature at present and is likely to have bugs. Please feel free to report them here:
http://www.gamefaqs.com/features/feedback/new.html?typeid=20 --- Um, not to criticize science or anything, but wouldn't it be easier just to call it "the pink one"?