The obvious examples are Dan and Jones, aka Howard Moon and Vince Noir from The Mighty Boosh. The two sets of characters are so analogous to each other (both flatmates with non-existent careers and polar-opposite personalities) that it almost seems like a Casting Gag. Their flat in Boosh is even in nearby Dalston.
Speaking of The Boosh, Saboo also turns up at Sugar Ape as Ned Smanks, but then he's much better known as either Thornton Reed or Maurice Moss.
Carrying on the Boosh connections, Nathan and Troll both appeared together in the "Fountain of Youth" episode, as the King of Xooberon and Banoo respectively.
Dr. Guy Secretan has a small but disturbing cameo as Rod Senseless, a deranged rapist pornstar. His erstwhile colleague Boyce also appears as The Weekend on Sunday's features editor Max Herbert.
Q has come a long way since his stint as Nathan's dogsbody.
...as has Matthew Horne since his time working behind the counter of a shop called, er, Bumphuk.
...and isn't that Sherlock doing Doug Rocket's accounts?
Pilot: The pilot episode was initially unaired, but released as an extra on the DVD. It's 40 minutes long, compared to 25 minutes for the regular episodes, and is essentially an early version of episode 4, with large sections of episodes 3 and 5 mashed into it.
Like episode 4, the main plot revolves around Nathan continually bumping Claire's latest film off, so that he can hit on Dajve Bikinus, only to make a twat of himself by copying Dan's "Geek Pie" haircut - the one that Dan is trying to get cut off when he kills the barber's cat.
Different parts from the following episodes are included:
Episode 3: After killing the barber's cat, Dan goes to Place to attend the 15Peter20 art exhibition from episode 3. In the aired episode 4, he goes to the bank for a loan interview instead. He's still completely covered in paint in both instances.
Episode 5: Claire's prostitution film with Mandy, including the subplot with Mandy blowing Nathan. This replaces the endless interviews of Doug Rocket in the aired episode 4.
Notable differences to the aired episodes 3, 4 and 5:
Dajve seems mostly interested in using Nathan for the acting role that he offers her, whereas in the main series, she seems a lot friendlier and more sexually attracted towards him.
Nathan ditches Dajve in the high street and runs off after seeing Dan approaching. In the aired episodes, Dan never appears, and Nathan instead continues to accompany Dajve to the hipster theatre.
Mandy is not a cokehead teenager, but just a fairly regular aspiring actress in her early twenties (played by Kate Fleetwood, instead of Ophelia Lovibond)
The Stanley Knives scene, where Nathan gets his Geek Pie cut, is extended considerably to show Troll's "snip stats" on a tablet, and Troll constantly having to stop Nathan from bopping his head to Jones' music, before getting pissed off and ramming a dummy into Nathan's mouth. We also get a previously unseen Liz White as a hipster cashier who calls Nathan "Nelson Bailey", seemingly out of malice, before charging him an arm and a leg on his credit card.
A brand new, unused scene at the end shows Claire's film being screened at Place and being largely successful with the crowd, to Claire's dismay, who thinks the praise stems purely from Mandy's tits and not from any artistic merit.
You Look Familiar: Ned and Rufus are both absent from the pilot episode, but the actor who plays Rufus, Spencer Brown, still appears as 15Peter20's PR manager in the art exhibition at Place. This part is played by Jolyon Rubinstein in the main series.