Above Comscore's European numbers  how ad impressions served up on social networks is exploding (North America looks pretty similar).  Facebook and online retail, led by the Groupon-driven couponing craze is up with the big losers being instant messaging and, gulp, eBay. Investors, beware. It’s becoming increasingly apparent that these deal-of-the-day sites like Groupon are starting to eat into the online auction market.  Traffic to online auction sites and eBay in particular fell 3.6 percentage points last year.