Factual error: This is a wardrobe error... in the next morning scene after William has been deflowered, he is still in his Fruit of the Looms, which have the name printed on the elastic waistband. Fruit of the Loom did not print their name on waistbands like this until the 90s, in the 70s they just had single blue and yellow stripes.
Trivia: Penny Lane picks up William to go see Stillwater at the Riot Club in L.A. In the very beginning of the scene in her car, a reflection passes up the windshield over William's face as they are driving. The Reflection is the prism and spectrum from Pink Floyd's "Dark Side of the Moon" album. There are no other reflections in this scene.
Trivia: When Penny Lane asks William to go with her to "wherever", she asks him twice. The first time William didn't like the way he said it, so he asked her to ask him again while the cameras were still rolling. Cameron Crowe like it so much that he kept the entire sequence in the film.
Trivia: This is the first Cameron Crowe movie not to feature a cameo by Eric Stoltz. Stoltz was supposed to appear on a theater marquee that said "The Crazy World of Eric Stoltz" but that didn't work out due to budgeting. Although, while the theatrical version doesn't feature Stoltz, Crowe stated in the "Untitled" DVD commentary that the Untitled version does include a reference of some sort to Stoltz, thus keeping the streak alive. Crowe encourages fans to try and find the reference in the film.