I really like this Coke video that's sweeping YouTube. It nails the brand idea (happiness). It's also and interesting blend of event marketing and viral marketing.
The basis of event marketing used to be to stage something provocative to get customers to in a specific location to experience the brand in a new and engaging manner. The event would be seen by the 500 or 5,000 people at the event, whether on a street, a campus or at a sporting event.
Social media changes everything. Now we need to think about event marketing as a form of mass media. Stage an interesting event that can be documented and seen by the 500,000 people who will view it and share it on Twitter, Facebook or YouTube. At last count Coke has racked up over 784,000 views so far. I would imagine that is slightly more than the number of folks on the campus where they staged the event.