It’s no secret that the media industry has become smitten with Twitter—just turn on CNN. So what’s all that free exposure worth? Forty-eight million dollars over the last 30 days alone, according to news monitoring company VMS, which bases the figure on the reach of all the Twitter coverage (It generated 2.73 billion impressions over the last month). AdAge puts the amount in perspective, saying it’s nearly half of the $80 million to $100 million Microsoft (NSDQ: MSFT) is spending to advertise the relaunch of its search engine Bing. And Microsoft is certainly not spending its entire marketing budget in one month. More perspective: Twitter has raised $55 million in funding.

Of course, it’s not clear how long the exposure will last. Says VMS CEO Peter Wengryn: “As we source some of the other phrases like LinkedIn and Facebook, they were hot and the ‘in’ thing at the time and certainly they don’t have the same sizzle they did today as they did in the first two or three months.”

But one thing that’s striking about the $48 million figure is that the exposure was likely even higher earlier this year—when Time featured Twitter on its cover under the headline “How Twitter Will Change The Way We Live” or when Oprah hosted Twitter co-founder Biz Stone on her show, for instance.

The media attention has been repeatedly credited with driving much of the microblogging service’s recent growth. But all the attention also may explain why such a high percentage of users abandon Twitter. Some people may have heard a casual mention on TV, decided to try it out, only to lose interest quickly.

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