Who would have thought rejecting a $6 billion offer from Google could have led to more money? Groupon, the social buying site, is pushing forward with its plan to take the company public, at an estimated value of $15 billion or more. The company raised a record $950 million from big investors, and has been discussing a public offering with bankers. Groupon is expected to make its public offering sometime this spring. After rejecting the offer from Google, Groupon has become one of the most-talked-about public offerings out there. The company, founded less than three years ago, has more than 50 million users worldwide and an annual revenue of more than $1 billion.