A favorite view of Spider-Man (at least in movies and games) is of the hero web-slinging his way through the streets of New York City. But what becomes of all the web ropes that Spider-Man discards as he moves from building to building? We don't see them hanging around the city, so presumably someone removes them.
Do people collect them as souvenirs? Does Spider-Man come back later to clean up after himself? Does the city employ a group of cleaners just to remove the webs?