This morning I reported at SEW blog on a Forbes article that says Yahoo! is testing a ppc algorithm similar to how Google AdWords works. The new pay per click model will use a relevancy factor, in combination with your bid price, in ranking your ads in Yahoo! Search. The test, code named "Project Panama," is being run in Scandinavia and will be working in the U.K. by July.
eWhisper at WebmasterWorld says we can probably see this in the US by September of this year. Most of the discussion in the thread is positive. This is a huge change and will affect you, forum discussion at WebmasterWorld.