When discussing his previous cases with Todd, Dirk mentions success with a case involving a couch, and another involving Thor, which are from the novel "Dirk Gently's Holistic Detective Agency" and "The Long, Dark Teatime of the Soul" respectively.
Dirk Gently's real name is Svlad Cjelli. Douglas Adams stated that the character of Dirk Gently was partly based on his friend, Michael Bywater.
In the driving scene, Dirk and Todd almost run over a man in the middle of the road. If you look closely, this man is actually Gordon Rimmer, a major linchpin of the whole series plot, and this is his first appearance. Talk about the 'interconnectedness of all things'! (Which is of course exactly what Dirk is talking about at that moment.)
Ty Olsson and Kavan Smith have both played Deputy Andy, the android deputy, in the Syfy channel series Eureka (2006).
Osric Chau, who plays Vogel, and Ty Olsson, who plays Dorian, have both also guest starred in Supernatural (2005). And though Osric plays an energy vampire in this series, Ty plays a traditional vampire in Supernatural.