Users can filter images according to the images' tags and ratings. You can find your blacklist on your user profile.
The blacklist works the same way as image tagging, i.e., tags are separated by spaces, and spaces inside tags are made with the underscore, e.g., would filter out all images with either or both of the tags "abuse" and "wall_of_text".
You can filter images according to the uploader with user= followed by the user's name, e.g., would filter out all images uploaded by Hewmon. Blacklisting a user also works for comments, i.e., if you blacklist a user, you won't see any of that user's comments either.
It doesn't work for anonymous users.
It doesn't let users filter for meta-tags other than user=.
It doesn't adjust navigation, e.g., if twelve pictures are filtered away from page one, the filter will bring over twelve pictures from page two to fill the space, but because the navigation is not updated, those twelve pictures will still be displayed on page two, and similarly if all pictures on pages one and two are filtered away, the same pictures will be shown on pages one, two and three. If all pictures are filtered away, and no pictures can be brought over from subsequent pages to fill the space, you will get an error (code CI01) - this is mostly a problem with image searches where the number of results is low. Note that this will never happen as long as there is at least one image to display after the filter is applied, so you're not missing out on anything.
If you find any other bugs or issues with the filter, please let me know.