With the recent ouster of Tom Freston, McGrath is one of the few MTV veterans still standing. With channels like Comedy Central and Nickelodeon, her MTV Networks holds a nearly 25% market share in cable ratings and ads—and brings in 70% of Viacom's $10 billion in revenues. But there is danger ahead as advertisers move online, where 25-year-old MTV lags newcomers MySpace and YouTube.