The creators describe the main theme of the show as failure: "This show is actually all about failure. Beautiful sublime failure. Every character is not only flawed, but sucks at what they do, and is beautiful at it. Even in the design, everything is supposed to be kinda the death of the dream world, the jet-age promises. It shows that failure's funny, and it's beautiful and it's life, and it's okay."
Brock Samson's devotion to Led Zeppelin surfaces in several episodes. Some references are subtle - when driving the Charger, Brock almost always is listening to facsimile Led Zeppelin songs - while others are more overt, such as Hank rifling through Brock's collection of "Zep" cassette tapes, or Brock drawing the logo of the band's label instead of completing the essay portion of a written exam. He even has a (currently incomplete) tattoo of the label on his arm.
H.E.L.P.eR. stands for "Humanoid Electric Lab Partner Robot." It's discussed during the audio commentary on The Venture Bros.: Tag-Sale: You're It! (2004) that Jackson Publick/Christopher McCulloch originally voiced the sounds for H.E.L.P.eR. Then Doc Hammer ran this through Soul-bot, a robot that they have at Astrobase Go! to give us H.E.L.P.eR. sounds. You can see Soul-bot at the end of every episode in the Astrobase Go! i.d. It was also discussed that they gave up making new sounds after a while and just use the same ones over and over.
The trivia items below may give away important plot points.
Doc Hammer is a fan of David Bowie and makes many references to Bowie in the show. In the episode "The Incredible Mr. Brisby", one of the characters mentions that he got a panda from David Bowie as part of a bet, but in the end of the episode, Molotov Cocktease was seen driving to return the panda to Bowie. In "Showdown at Shadow Creek, part 1", David Bowie makes an appearance (but not voiced by Bowie, but assumed to be voiced by James Urbanski) and is in the Monarch and Dr. Girlfriend's wedding, giving Dr. Girlfriend away at the wedding, but the wedding is interrupted by Iggy Pop and Klaus Nomi, who are working for the Phantom Limb. When the wedding is crashed by Phantom Limb, it is revealed the Bowie is the current leader of The Guild of Calamitous Intent, known as The Sovereign. He barely escapes assassination attempts by Klaus and Iggy. In "O.S.I. Love You", it is revealed by Monstroso that the Sovereign may not be Bowie, but a shape shifter who met Bowie and uses his form. This shape shifter is said to be the creature on the cover of the album Diamond Dogs, and perhaps the woman on the cover of Pin Ups.