These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Cabin Pressure
Hilarious in Hindsight: While playing an on-flight game in 'Fitton', Martin (played by Benedict Cumberbatch, from BBC's Sherlock, which hadn't been announced at the time) references 'The Hound of the Baskervilles'. Even better after series 2 of that show, as the context of the reference is removing one letter from books to make them different, and he changes 'Baskervilles' to 'Baskerville'... just as that show did for its adaptation of the story.
Stephanie Cole is going to be in an adaptation of "The Lady Vanishes," which was part of the Hitchcock game in "Qikiqtarijuaq."
Launcher of a Thousand Ships: Martin appears to be the fandom bicycle judging by the fanfiction (not helped by the fact that he is played by the very attractive Benedict Cumberbatch). The most popular pairing starts with Martin/Douglas, then Martin/Arthur and goes from there. There are a couple of Martin/Diego (from 'Johannesburg') fics, and Martin/Molly Hooper and Martin/Henry Knight are both becoming popular.
Periphery Demographic: Cabin Pressure is a fairly gentle and traditional Radio 4 comedy, Radio 4's audience being memetically middle-aged, middle-class and terribly English. Presumably thanks to the presence of Benedict Cumberbatch in the cast (as well as the program being good enough to sustain a devoted following, of course), the show has attracted quite a fandom on the notably international, all-comers, young people jamboree that is Tumblr.
The Woobie: Martin, mostly due to his luck or lack there of.
Most obvious in 'Qikitarjuaq', 'Fitton' and 'Limerick' — aside from the fact that Martin had to retake his CLP seven times, with even his own family not believing he'd manage it, he also has to live in the tiny attic of a student house, and because Carolyn doesn't pay him for being a pilot, his only monetary income is the jobs he takes as a stupidly cheap man-with-a-van which he has to fit around his MJN flights.
A passenger makes him cry in 'Boston.'
Arguably Arthur in 'St Petersburg'. His frantic attitude and desperate desire to please his father are completely out of character, and even Martin and Douglas notice it.
Martin: What’s he like then, Mr Shappey?
Douglas: I don’t know, I’ve never met him either, what’s he like Arthur?