Invisible Advertising: The amount of advertising the show gets is woefully out of proportion with how high its ratings are; it's one of the highest rated shows in the country, let alone on CBS, and yet it's rarely advertised except on the night that it airs and it's often absent from the group CBS network promotions.
The opposite was true when the show was first introduced. CBS promotions went into overdrive during the summer of 2011 to hype the show up, with POI ads outnumbering those for fellow rookie Unforgettable by about two to one. Ironically, it had the opposite effect in the ratings - the premiere dropped nearly forty percent in 18-49 from the second half of a special hourlong episode of The Big Bang Theory (5.1 to 3.1), and was outrated by all but two of CBS' other Monday-Thursday dramas. Given the pedigree and heavy marketing, this was considered a disappointing start. The only upside is that the show stayed in the general vicinity of this number for its entire run on Thursdays, while several other CBS shows fell off.
Sadly, season three was moved to Tuesdays at 10pm, a budding curse slot for the network which has killed almost every show placed there since Judging Amy went off the air, and is down year-to-year. Facing Sons of Anarchy, one of cable's most popular series, which has grown year-to-year for three straight seasons, isn't helping. Neither is the continuation of this trope in the new slot.
Mean Character, Nice Actor: True, this can be said of anyone who isn't a serial killer but plays one, but there are some notables.
Jim Caviezel, playing an Anti-Hero killing machine is a devout Catholic with two young children.
Enrico_Colantoni playing affable but ruthless mob boss Elias is a spokesperson for the Tema Conter Memorial Trust, which helps first responders and such with post-traumatic stress disorder.
Robert John Burke, playing the memorable and vile Patrick Simmons spent several days at Ground Zero after the September 11 attacks assisting with the search and rescue. He has since become a New York State certified firefighter. He also recently traveled to New Orleans to assist in the re-building of New Orleans fire houses.
John Nolan who played Kara's employer in "Dead Reckoning" is the uncle of Jonathan Nolan.
Paul Sparks (Wilson in "Relevance") is married to Annie Parisse (Kara Stanton).
Throw It In: Reese kissing Carter at the end of "The Crossing" was improvised by Jim Caviezel.
What Might Have Been: The original script for the Pilot episode revealed all of John and Jessica's backstory in that episode, and would have also included a scene where Finch provides Reese with an apartment to live in. The John/Jessica backstory was cut down and then spread out over the course of the first season, and the apartment became a birthday gift in "Many Happy Returns".
Carter's pursuit of Reese was originally intended to continue over the course of the whole first season, but she ended up joining the team mid-way through due to pressure from CBS.note Mileage Varies on whether or not it was a good move for her to join so soon.
Why Fandom Can't Have Nice Things: The reaction to the ending of "The Crossing" has forced the show runners and Taraji P. Henson to go into something akin to damage control mode.
Taraji P. Henson: "That's why people are so distraught today. And that's what art is supposed to do: It's supposed to make you feel. You're supposed to be mad and want to throw a glass and yell, "Goddammit, I'm not going to watch this show again." We did our job."
Jim Caviezel is ambidextrous in real life.
While on location in New York City, Jim Caviezel saw some punk beating his girlfriend and "intervened".
An incident which has caused some fans to come to the conclusion that he is John Reese.
The (stolen) black Porsche that Reese drives in "Bury the Lede" actually belongs to Jim Caviezel.
Which incidentally implies that John Reese stole Jim Caviezel's car.
In the episode "Critical" Person of Interest became one of the first mainstream US dramas to portray a married same-sex couple.
Kara Stanton was killed off earlier than expected because Annie Parisse is already on The Following. Ironically, her Following character, Debra Parker, was dead by the end of season one.