"Who gon stop me," from Jay-Z and Kanye West's Watch the Throne, begins with an orbiting, distorted vocal sample, then explodes into a rush of quaking bottom-end and pulsating, chunky mid-range. These are the blatant hallmarks of dubstep, the floor-shaking, multifaceted electronic music that began on South London pirate radio nearly a decade ago and now peppers U.S. pop radio. If you're looking for a bellwether moment to signal this genre's American takeover, you could do worse. "Who Gon Stop Me" won't break dubstep, though, because dubstep, depending on your perspective, already has arrived broken, dead, or unrecognizable. Similarly, recent dubstep-inflected pop tracks by Britney Spears, Snoop Dogg, Rihanna, and Korn are mile markers, not destinations.