This is by far my favorite add-on. Not only does it allow you to keep track names that have killed you but it also immediately notifies you if an enemy gets within 100 yards of you. Having this add-on completely changes world pvp and makes it almost required.
I can literally walk into BRM and instantly see everyone from UBRS to BRD. They target me and I target them. It takes away some of the surprise and it also changes the dynamic. It lets your average joe whom never watched over his shoulder before be aware and it allows high level players to roam through zones and instantly scout people to gank.
I love it but it feels like its too powerful. It also takes away from hunters/druid tracking abilities and makes it nearly impossible for lowbies to hide.