MSN recently created a website in conjunction with Sprite — it’s called "The Wall" [1].
Then, MSN hired a Seattle agency known as the Wexley School for Girls to help them launch the website in a loud way, on the ground, guerilla style, in Atlanta where Sprite (aka Coca-Cola) is headquartered.

Wexley held a design contest, received entries from all over, selected 3 winners, created gobo’s with the artwork on them, and "tagged" the city using high-powered light projectors, throwing artwork randomly all over town.
The best projections were at World of Coke and a selection of hits on the sides of huge buildings -- one example was like 80 feet tall, 50 feet of image. Caused a traffic jam. Supported by radio remote, DJ, etc.


The client is now considering rolling it out to different cities - TBD.
Links:
[1] http://thewall.msn.com
[2] http://technorati.com/tag/Ambient & Guerrilla
[3] http://technorati.com/tag/telecom & dotcoms (ads)