Late Wednesday, YouTube announced that it has more than 1 billion unique users every month. That puts YouTube in the same club as Facebook, which surpassed 1 billion monthly users last October.

YouTube has long been the most popular video site beginning in the days when it was mostly user-contributed videos and premium video sites—such as Hulu—had yet to appear. These days, YouTube is the go-to site for movie trailers, music videos, the occasional pirated TV episode, as well as cats fighting printers and skidding across linoleum floors.

The Google-owned site attributed its large growth to Generation C, a term coined by metrics firm Nielsen to describe American aged 18 and 34. “Born sometime between the launch of the VCR and the commercialization of the Internet, Americans 18-34 are redefining media consumption with their unique embrace of all things digital,” Nielsen said in an early 2012 study. On YouTube, Gen C are the folks watching YouTube videos across multiple device types including smartphones, tablets, and PCs. Not coincidentally, this crowd also happens to be big on video creation, sharing, and curation of favorite YouTube clips.

During 2012, the number of Generation C viewers watching YouTube on mobile devices equaled YouTube’s desktop viewership, according to Google. Around 67 percent of Generation C also watch YouTube on more than one device, compared to 53 percent of the rest of YouTube’s viewership.

The trend among YouTube viewers relying on mobile devices will probably only increase in the coming years. About 37 percent of American teenagers (aged 12-17) owned smartphones in 2012, according to a recent study from the Pew Internet and American Life Project. And half of those smartphone-owning teens use their phones as the primary way to get online, the study said.