It's the place where Web stars are born, music and film careers are launched and some single people manage to find mates. This exploding social-networking site is now the most popular website in the U.S., boasting some 100 million registered members. In the last year, traffic jumped from 17 million unique visitors per month to 54 million more than Yahoo gets some weeks. As a member (it's free) you can post all sorts of content blogs, photos, videos, MP3s to your profile page; get a few hundred thousand other "friends" to link to it and Bam! you're on the pop-culture map. Marketers may even come calling, hoping to piggyback on the exposure. MySpace's wild popularity has inspired a slew of startups to create features and applications specifically for MySpacers like Rojo Networks' "Nooz" ticker, which links to the day's top stories, based on how many other members are reading them. In July Web humorist Ze Frank hosted an ugliest MySpace page contest; David Lehre's parody, "MySpace, The Movie," is a YouTube favorite. There's even a mobile phone the Helio Hero offering one-button access to MySpace so you can view pages and respond to friends on the go. Think MySpace is too "young" for you? New social network Eons is targeting the 50-plus crowd.