http://investor.groupon.com/financials.cfm
Groupon had (in q3 2013, the latest I could find) 595M in revenue and 14M in operating income, an EPS of 0.02 excluding "excluding stock-based compensation and acquisition-related benefit", and 1.1B in the bank.
Not a smashing success, but is it a failure? The jury is still out on this, imho.
Given that success and failure are both relative terms, I would say Groupon is only a "failure" if you're measuring it by the perceived success it would have. So I would say that if you expected Groupon to be a $10bil company, they are a failure...but if you expected Groupon to be a normal company of a few million in revenue, then they are an amazing success.
Although Groupon may not have had the most lucrative business model in the world, I still feel like they've done a great job at "sticking to their guns" and not trying to enter all kinds of other markets (and failing miserably).
In less than one year