Script Summary: De-emphasize viewed stories and remove entries for particular domains
This script uses jQuery, since Reddit was recently updated to utilize that framework.
The story block of visited links will have their opacity set to 0.2 once the page is loaded. Clicking on a link will also result in the opacity change. Hovering over a story block will temporarily restore its opacity to 1.0.
The variable site_blacklist can be set to a regex expression to match domains for exclusion. For example, site_blacklist =/example.org|yahoo.com|digg.com/ig; will result in stories from example.org, yahoo.com and digg.com to be removed.
The script is completely public domain.