This week, YouTube celebrated its ninth birthday. As you would expect, the site put together a video with some of its most well-known stars and songs. The final product: an epic karaoke mashup. At this time, the video is climbing toward 500,000 views, but we all know YouTube will promote it like crazy. If it isn’t already on your YouTube homepage, it will be soon. But we decided to post it for you anyways. Enjoy!