Defictionalization: In spades. The actors perform in character in live shows. They've recorded three albums, made music videos, and appeared on countless radio and TV shows. They even have a feud with Marty DiBergi about their portrayal in the film, going so far as to take offense that people find the film humorous. DiBergi has at times responded to these claims. Their audio commentary on the Special Edition DVD is also fully in character, arguably constituting a movie in its own right. The song "Gimme Some Money" was even covered for a Citi Bank commercial!
The venues they play in the movie are fictitious. However, in 1989 an actual Shank Hall opened in Milwaukee. Their logo includes a miniature Stonehenge and there's a shrine to Spinal Tap in the club.
Also, amps that actually go up to eleven are now available.
"Up to Eleven" itself became a legitimate English phrase with its inclusion in the Oxford Dictionary.
You can buy "Nigel's Skeleton" Shirt online.
In many ways, Spinal Tap has become so iconic that the boundary between real and fiction is blurred for many fans and performers of the genre, even if only to maintain The Masquerade.
DVD Commentary: The original commentary for the film released on DVD by Criterion was played straight. When MGM re-released the film on DVD twelve years later, Guest, McKean and Shearer recorded a commentary in character, spending most of it ripping director DiBergi for the "hatchet job" he produced.
Fake Brit: Harry Shearer and Michael McKean. Christopher Guest, on the other hand, has dual American-British citizenship and is now a British Baron. The accents of the cast were apparently good enough to fool British audiences.
A year after a demo reel of the film was produced in 1982, Black Sabbath's Born Again tour featured a Stonehenge set that was also marked up with the wrong measurements on the schematics (meters instead of feet, resulting in a 50' tall stone instead of a 15' tall stone).
Boy George got stuck inside a ridiculous huge prop onstage during a number.
David has a line where he'd been planning on doing a collaboration with the London Philharmonic. 15 years later, Metallica came out with "S&M," a live album featuring the band playing alongside the San Francisco Symphony. Not to mention that there's now an entire genre of Symphonic Metal...
One of Spinal Tap's drummers died in a "bizarre gardening accident"; Toto drummer Jeff Porcaro was reported to have died after inhaling insecticide that he had been spraying in his garden. However, coroners later put his death down to a heart attack due to cocaine abuse. Family and friends disputed this, claiming that he had a family history of heart conditions and was not a heavy cocaine user.
Similarly, Ronnie James Dio injured his thumb moving a garden gnome. He even referred to the incident as a "bizarre gardening accident".
Likewise, the drummer who died "choking on vomit." John Bonham died this way, after a night of heavy drinking. So did Jimi Hendrix. Although it wasn't "somebody else's vomit."
Between 1983 and 1984, Marillion burned through three drummers in rapid succession after firing Mick Pointer before finally settling on Ian Mosley. Notably, they did this in between their first two albums, Script for a Jester's Tear and Fugazi.
In the film the band's album Shark Sandwich is given a two-word review in Rolling Stone: "Shit Sandwich." Years later, Quiet Riot's fourth album Condition Critical was given a similar two-word review in Rolling Stone: "Condition Terminal."
In 1992, the German heavy metal band Headhunter released an album titled A Bizarre Gardening Accident.
There are now guitar amplifiers that actually go to 11... and beyond. Marshall released models in the 90s with '11's on the faceplates specifically to replicate the ones in the film. Extends to some audio recording equipment too, with SSL mixers' monitor (speaker) volume settings and Pre Sonus audio I/O interfaces headphone settings.
Authentic metal legend Ozzy Osbourne is on record as saying that This Is Spinal Tap is a worryingly accurate portrayal of what it was like being a rock star in the 1980's. Specifically, although it hadn't happened to him, he describes the scene where the band get lost backstage and claims that he "could all too easily imagine that the same thing had actually happened" in real life, among other examples.
In fact, when he first saw the film, he didn't laugh once because he didn't realize it was a satire.
Heart's Ann Wilson said that she watched it and said, "Oh my God, that's me!"
KISS's Gene Simmons has said that the "Hello Cleveland" sequence happened to Kiss, though the specifics were different. Their dressing room was on the fourth floor, and they went down to the first floor because that's where they thought the stage would be and found nothing. They tried the second floor, nothing. Meanwhile, they could hear themselves being announced on the third floor.
Re. the comment —>David:37 people have been in this band over the years! Coincidentally, this is about the same number of personnel who have been with space rockers Hawkwind over the life of the band. And a cursory look at the Hawkwind personnel list shows a disproportionate number of these were drummers. Hawkwind's stage sets and lasers were also so ambitious they blew the fuses at many venues.
Members of Jethro Tull played a prank on their frontman, Ian Anderson, during one of their concerts. They lowered an 18" model of Stonehenge from the ceiling in mid-song, and the roadies danced around it.
Non-Singing Voice: Averted. The three leads play their own instruments and do their own singing. As stated elsewhere, they've done countless live performances demonstrating their musical talents.