The viral marketing campaign of the year has to be the "I'm Making a Difference " campaign from Windows Live Messenger. The marketing idea behind the program is to encourage people to make greater use of the Microsoft platform for instant messages. To do this, they are asking all users to select a charity of interest and append that logo to your IM name.
Once you select your charity, Microsoft will make a donation for every IM click which in turn is a percentage of the revenue generated by advertising displayed on the interface. This is a brilliant program as it works functionally and emotionally. Functionally it generates increased click through rates and provides a distinct reason to choose Messenger over AOL and Yahoo. Emotionally it makes the user feel like they are doing something beneficial while projecting an image of someone that makes good choices that benefit others.
While we have seen many viral marketing programs that involve gimmicks such as dancing elves, morphing Simpsons and Men dressed as women, this program rises above the rest. The Microsoft program is definitely the best viral marketing program of 2007 and one of the best branding programs as well.