As of March 2015, there are over 19,000 downloadable mods on Garry's Mod's Steam Workshop page.
Numerous YouTuber's such as VenturianTale, VanossGaming, I AM WILDCAT, H2O Delirious, PewDiePie, Markiplier, and Daithi De Nogla have done Garry's Mod videos on their channel.
This game is known for an Anti-piracy method where cracked copies would get an error stating, "Unable to Shade Polygon Normals." This would only appear in pirated versions of the game and if someone asked for help to fix this "error," they would immediately get outed as a pirate. Over 2,500 pirates have been caught by this error.