I've written before that we'll see a move away from bidding on keywords in favor of paying for leads, regardless of the terms used by those leads/searchers to find us. Now Overture says it's something they are considering: flat rate pricing to make search easier for small and medium sized businesses. More from this ClickZ article, Yahoo!'s Overture Looks At Simpler Models to Court Advertisers.
I can see that coming -- just as I can see flat rate pricing making life easier for big advertisers, as well. If you're Nike, and you want to be tops for shoes, writing a big giant check for guaranteed top placement makes a lot more sense that trying to manage thousands of keywords. It'll come.