There have been several examples of the trend towards collaborating with actual customers to build a brand or specific marketing campaign, such as Doritos' "Crash the Super Bowl."
Now there is an actual tool that can help you organize and launch a contest in which your customers can compete with their own ads about your product or service. Zooppa - "People-powered brand energy" - provides templates and tools that make it easy for customers to share their interpretation of your brand. Here's one for Brooks bio-degradable running shoes.
Zooppa also enables you to set up contests with cash prizes for the best ad, like this one for Mini Cooper.
Turning the reins over to customers isn't necessarily the best or only way to build a brand, even in our current social media-crazed world. But it is a very cool way, as part of an overall strategy, to get them intimately involved with your message. And who knows, they might create a viral hit that your agency never would have.