I've recently purchased an space upgrade to my picasa account and the checkout process was, not surprisingly, based on Google checkout. Google using its product internally might not make headlines but it reinforced one of my long time established beliefs in software development about eating-one's-own-dog-food. If you don’t find value in your <T> (software as an example) to use it frequently and rely on it, you should not expect others to find it fascinating.
This is one of the problems I have with Microsoft Live i.e. I believe the main problem lies in the core of the search algorithm and results which turns people away. I was recently looking for Juval Lowy’s WCF 3.5 article published in the MSDN Magazine and here are the results from both Google and Live with the same search keywords. One brings me the pertaining and relevant info in a clean and concise way, the other does not.
That’s why I think YHOO purchase would not significantly give Microsoft an edge in the search space because its core competency in search R&D is not as strong as its largest competitor. Two mediocrities do not create one greatness IMHO. This further trickles down to other sources of revenue which heavily rely n search technologies nowadays such as web advertisements. And like my buddy Nauman said "Google could be the beneficiary here as this could start a mass exodus of talented developers if the deal go through."