I'm no longer a customer of Groupon. The plural of "anecdote" isn't "data", but I don't know of any company where customer acquisition isn't a major cost. The traditional business school number touted is that is costs 10 times as much to acquire a new customer as it does to maintain an existing customer.

EDIT: I know I may have counteracted my own argument, but my point was that customers are expensive, and the costs don't go away, even if they lessen.

If you look at many subscription-based businesses (newspapers, cable providers, mobile voice/data companies), you'll often see businesses where the cost of acquisition is pretty low compared to the life-time value of a customer. Newspapers (pre-Web) are a particularly good example of this - most of their costs were in production/distribution. Acquiring a customer was relatively cheap and churn relatively low.

So anecdotally, there are historical business models that feature low acquisition costs & low churn.

There will always be people who scour coupon sites for deals, even taking into account natural customer churn. It's conceivable that Groupon could be the Google on coupon hunting.

However the number of coupons available isn't going to increase forever, and may well already be in decline (for some measure of businesses using Groupon compared with deals offered).

This is because those businesses see Groupon as a way to infrequently attract a large number of people to try their products at a price that they would not be able to sustain for other marketing models such as advertising.

The only way Groupon can "grow" is to continually reach new businesses to ensure that the number of coupons available is high. However, eventually the well will run dry.