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, Nathan continually bumps Claire's latest film off, so that he can hit on Dajve Bikinus, and also makes 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 other episodes include:
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, replaces the endless interviews of Doug Rocket in the aired episode 4.
Notable differences to the real 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, it comes across as purely sexual attraction towards Nathan.
Nathan ditches Dajve in the high street and runs off, instead of accompanying her 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.