She bases that assertion on the behaviour of the nearly 500 million souls who gather on Facebook.
Speaking at the Neilsen Consumer 360 conference in Las Vegas, Ms Sandberg claims: "If you want to know what you'll be doing tomorrow, look at what teens are doing today."
Ms Sandberg, who you can watch on YouTube, claims that only 11% of teens use e-mail, preferring text messaging and social networks.
Even though 90% of e-mail may be spam or other useless twaddle, it is hard to believe it is nearing its sell-by date.
A report by the Radicati Group says that e-mail is still on the rise and projects that e-mail accounts will increase from 2.9 billion today to over 3.8 billion by 2014.
At the same time, social networking is predicted to climb from over 2.1 billion accounts in 2010 to over 3.6 billion by 2014.
Do you agree that platforms like Twitter and Facebook are sounding the death knell for e-mail? And if it were to die off, would you miss it?
