"...Jarvis wrote about a bad experience he had with computer giant Dell's customer service, creating an avalanche of negative comments about Dell and bringing to light hundreds of bad consumer experiences with Dell's support staff."
Link - bolding's mine, to help explain the Snowball Effect. It's viral, yes - but it's not about "viral marketing". It's about very real value creation through viral dynamics - value that would otherwise never be created.
Read the quote again - it should be clear that this is the case. Jarvis's story caused new information (not just marketing blurbs) to be revealed and to snowball - information that effectively transferred value from Dell to consumers, and to it's competitors.
So the Snowball Effect is not not about Blair Witch (etc) style buzz - it's about value itself snowballing. In fact, Snowballs are a hyperefficient strategy for value creation in a world of connected consumers, but we won't get into the how and why here.
The point I want to make is simple: the Dell case is a very nice example for incumbents across industries that this is binary choice, a zero sum game: either you leverage Snowball dynamics, or you get commoditized by them.