Not only is their accounting on customer acquisition bogus, but how do they possibly value these customers? FTA:

Groupon's subscriber count -- the one Mason says it is spending aggressively to beef up -- now stands at 116 million, up from 83 million at the end of last quarter. Among those subscribers, 23 million have purchased a Groupon at least once.

So they have 116 million "customers," but less than 1 in 5 of those have ever actually purchased a deal?

Plus aren't Groupon's customers really the businesses paying for the Groupons, not the millions of subscribers to their e-mail list that apparently don't even purchase anything from Groupon? Seems to me that the "customers" they're referring to is really the product they're selling, and at a huge loss apparently.