Tyson Food, a US convenience food producer (chicken nuggets etc.) found a great viral marketing idea: They run a hunger relief campaign in Massachusetts. The company encourages readers on their campaign blog to comment to their action and for every blog comment they donate 100 pounds of food to the Greater Boston Food Bank. Originally they spoke about a truck of 35,000 pounds to fill. Within a five hours they had more than 700 comments and they decided to fill a second truck.
What a cool idea from a marketing perspective - whoever writes a comment, even a few words, stays a bit longer on the website than they would usually. And I looked up the corporate website because as a European I did not know them. Now I know them.
If it serves a good cause - the better.