A survey conducted Dec. 4 to 7, 2009 showed 28 % of shoppers who have already started buying gifts were influenced by social media, according to a report issued by the research firm comScore Inc. Of that total, 13 %said they were influenced to buy a product by reading an online consumer-generated review, while 11% were influenced by an expert review. 6% were influenced by friend’s status update on Facebook, while 3% said they followed the advice of a Twitter tweet.  7% of the respondents joined a retailer’s Facebook fan page, and 5% began following a retailer on Twitter so they could get special holiday offers and discounts. Story at SFGate.