Here are some links to articles discussing Groupon:
New York Times: http://dealbook.nytimes.com/2011/11/23/as-investors-flee-groupon-outlook-for-i-p-o-s-darkens/
Bloomberg: http://www.businessweek.com/news/2011-11-23/groupon-shares-plunge-below-ipo-price-3-weeks-after-offering.html
Mercury News: http://www.mercurynews.com/financial-markets/ci_19401073