Factual error: If the Vorgon Destructor Ship was as massive as portrayed, then as Ford and Arthur look up at it, it should have been reflected in Ford's shades. Instead, all that is seen is the demolition equipment and open sky.
Continuity mistake: When Arthur breaks the arm of the chair as his brain is being taken, the arm is strapped to his wrist. A second later the strap and broken arm are gone.
Slartibartfast: Ever heard of a place... I think it's called Norway? That was one of mine. I got an award for it.
Trivia: In the planet construction facility, one of the planets resembles Douglas Adams's face.
Question: Anyone who's read 'Life, The Universe & Everything' will now why the bowl of petunias thought 'Oh no, not again' just before it plummeted towards Magrathea, but had Douglas Adams already conceived that backstory and just couldn't fit it in to the narrative at the time or was it something he only came up with when writing part 3?
Chosen answer: Because it was a radio show originally, Douglas Adams would write broadcasts from show to show. He did not know where something would lead, which let the plot become random and funny. So ultimately it was originally created to be funny, then he found a way to link it back in later.