Is the hit single back? Consumers, propelled by the ease of buying digital songs piecemeal, have increasingly decided that the single unit of music is their unit of choice, noted music writer Tom Ewing in The Guardian last week -- just as hard-partying pop star Ke$ha broke the one-week record for digital downloads sold by a female artist. Ke$ha's ode to decadence, Tik Tok, now in its third week at Billboard Hot 100's No. 1, sold a whopping 610,000 copies for Sony (SNE) Music Entertainment's RCA imprint during the chart week ending Dec. 27. That's the second-highest single-week sales total for any one song, second only to Flo Rida's Right Round, which sold 636,000 copies last February.