Yahoo! has sent out a newsletter saying that the customers that U.S. Sponsored Search Listings will no longer be available on MSN. The newsletter read-
MSN's U.S. search distribution agreement with Yahoo! Search Marketing ends this month, and Yahoo! Sponsored Search listings will no longer appear in MSN's U.S. search results. Although we regret the loss of MSN as a distribution partner, it was not unexpected, and we do not anticipate a significant change in the total amount of traffic to our advertisers as a result.
We expect that MSN will continue to display Yahoo! Search Marketing Content Match listings in the U.S., and Sponsored Search listings in non-U.S. markets, beyond June 2006.
As MSN has been enabling the sponsored search side of MSN Search and Windows Live Search with Microsoft adCenter, this seems like Yahoo! & MSN are parting ways.