Anal retention isn't an attractive trait in human beings and so much less attractive in multinational corporations like Microsoft.
So we suppose Microsoft is to be applauded for redesigning its flagship search machine Bing! and puttling a limit on how long it will hang onto user data.
Part of the reason it's making this move is because there's a European advisory group made up of European Union members that don't want individual data to be held for use in advertising and marketing.
Microsoft has moved faster than Google - it was keeping data for 18 months. The company that is not "evil" and the company that doesn't have any morals, Yahoo! haven't taken steps to act in accordance with the EU's wishes.
Only the unduly cynical would think that the reason Microsoft is being so proactive on the privacy front is because it's already had a lashing from the EC which involved it paying lots of money.
The EU Article 29 group are advisory, but the European Commission will have the power to start investigations into privacy and will have teeth to bare, if necessary.