Everybody it seems wants to go viral these days, and it can be a big brand boost – remember Burger King’s Subservient Chicken? But in the new world, viral contagions can cut both ways. Witness Dave Carroll’s “United Breaks Guitars,” a melodic, frontal assault on United Airlines. The song and accompanying YouTube video chronicles a recent flight that left Carroll with a broken Taylor guitar. Posted just last Monday, three days later it’s already past 500,000 hits and 3,000 comments.

Less than stellar customer relations is certainly not a new phenomenon, but companies’ best learn that the ability of slighted customers to share their rage over poor treatment has taken on new, virulent dimensions. For sure, twenty years ago Mr. Carroll would have been no less pissed off at the “friendly skies” carrier. Still, his recourse typically would have been a cathartic rant to his wife and maybe a stern letter to customer service the next morning. Today, on his way to long-term parking he’s already called them out with a Tweet, a Facebook status update and a blog post instantaneously from his Smartphone. And, if he’s really fired up as Dave was, in a few hours a well-produced and entertaining music video is blasting the company for thousands of eyes worldwide.

Word of mouth, viral communications has always been the most powerful kind of advertising. What’s new is that the “mouth” is now an instantaneous, global megaphone in the hands of a skilled user. We’re sure United wishes they had taken better care of Dave Carroll’s guitar and accidents do happen. Next time though, they might want to think about taking better care of Dave Carroll – or if not, maybe make sure they damage his laptop and I-phone too!