I think it's difficult to say whether or not the rapid growth strategy was Groupon's best option in their early stages. The low barrier to entry means that a well-funded, well-operated clone could conceivably outshine Groupon before they could scale a profitable model.
would be interesting to see the various balance of profitability and growth of competing groupon clones. maybe groupon can shift their emphasis from growth to profitability before time runs out.