There's no need for corruption of the organic results if the ads are more prominent, and if the ads are satisfying users' needs in the same way that Yellow Pages ads and classified newspaper ads did in the print era.
I've seen a LOT of SEO companies diversify from straight-up SEO (organic listings) to PPC management in the last 12 months. In 5 year's time, I wonder how much we'll be talking about SEO for commercial searches. "Remember when clicks were free?".