The Kilroy plugin idea came out of a conversation I had with Luke Cross at Jerry's Retreat in Oaxaca. The idea is to provide a means by which visitors can simply make their presence known -- i.e. that they read a post -- even if they don't have anything to say. In a sense, by logging against some identifier, the effect should be the same as scrawling "I was here" on a wall. It's about shared, albeit silent, presence.

See also: Yellowcard WordPress plugin.