"So don't believe anyone who tells you they know what Groupon's worth. They don't. All they know is what their estimate is of what Groupon is worth. And, unfortunately, the range of "reasonable" estimates of what Groupon (or any stock) is worth is wide enough to fly a 787 through."
Valuation is a very subjective analysis and is a little bit art and a little bit science. We won't know Groupon's IPO valuation until it actually prices.