Music sites and web media watchers are atwitter about Yahoo's impending launch of what it hopes to be rival to Apple's iTunes music download service. A CNET report indicates the launch has been delayed to the end of March. Yahoo has enormous quantities of unsold ad inventory on its main web portal that it employs to promote its own lines of business, effectively giving it one of the largest and loudest channels to promote its own music service. Sony's and Microsoft's own online music retailing efforts haven't begun to visibly affect Apple's domination of the marketplace, but those firms have not dedicated tens of millions of dollars of media weight against their projects.