Groupon is a joke
it's losing money, has 100s of new competitors, some of which are well established *local* search portals, the deals suck, are luxuries that can be gotten for the *discount* price, usually at a closer location
as the article says, it's business customers aren't generally seeing the ROI they've been hyped to expect, and I suspect many, like me, subscribed to Groupon emails just to see what the hype was about, then unsubscribed a couple of weeks later after not seeing one *deal* of remote interest
beware when a business and it's venture capital is being spent mostly on sales staff and advertising-marketing .. it is not a business model .. just clever hype that will wear off
it's not like offering coupons for local business on the internet is a new concept, or that it is quite effective to do so on your own local business website .. on your Google Places page .. or offer discounts for services on Craigslist ( to name 3 common methods )
if you need Groupon for promotion, you are doing your internet marketing poorly otherwise