Michael Gray believes contests and incentives can become powerful link-building tools that help improve organic search engine rankings. Gray writes that typically links become worth more to the company than the cost of the prize, due to the rankings they can generate. URLS should also be another consideration that can improve rankings tied to contest incentives.
But don't make the mistake of leaving up old content on the page after the contest ends. Gray suggests leaving the page in place and replacing the information with different content.