Since it launched in 2005, YouTube has become one of the few Internet properties that's much more than a domain name. Like Google , Facebook , Wikipedia, and Twitter , YouTube has become an essential service of the Internet. It's a utility, a social network, a search engine, a source of online storage, and an endless source of consternation for content owners. Some quick numbers:
YouTube now gets 2 billion views per day, 30% of which come from the U.S. The three most popular videos are Lady Gaga's "Bad Romance, " at 196 million views and change, with "Charlie bit my finger"  and "The Evolution of Dance"  following behind at 186 million and 143 million, respectively. About 24 hours of video are uploaded every minute these days, and it'd take 1,700 years to watch all the video currently available.
The challenges YouTube faces in the future are both familiar and foreign. How to make money, for one thing, a challenge the site has not yet overcome (that's about the nicest way I could possibly say that--it's YouTube's birthday, after all, and I don't want to be rude). How to provide mainstream, for-profit content is another challenge, one that's the subject of constant work, from Vevo to the new movie rental service.
Then there's the challenge of the "third screen." YouTube has already conquered the first two; the computer was the first, and fell easily enough, while the mobile device was beaten thanks to the iPhone and YouTube's sister product, Android. But the TV, the third screen, has never successfully been defeated by a computer product, including Boxee, Apple TV, and Windows Media Center. According to the New York Times , Google will be announcing more details on their attempt  at the I/O conference this week.
For their part, YouTube is celebrating the milestone with a special commemorative site , featuring guest curators offering their favorite video picks (among the curators are Conan O'Brien, Pedro Almodovar, and LonelyGirl15). Conan's take? Our nation's obsession with YouTube is "probably why our country's economy is in the toilet," because we're all "watching monkeys in propeller hats flush themselves down a toilet" (parallel!). So from us, happy birthday, YouTube.