In 2008, a European Union panel of privacy regulators asked Google, Microsoft, and Yahoo to eliminate all online query data after six months. This data, which is valuable for the companies running search-engines, includes a computer's unique identification number, location, and the search queries. The Article 29 Working Group held a hearing with representatives from the search engine companies in February 2009, and had established a deadline of the end of January 2010 for each company to respond.

With the impending deadline, and in the hopes of averting a possible new European regulation, Microsoft has just agreed to comply with the Article 29 Working Group panel's directive, and discard user's I.P. addresses collected through its Bing search engine after six months. Previously, Bing had been keeping user data for over eighteen months. Although Microsoft has agreed to erase the I.P. addresses, it plans to retain cookies and other session identifiers, which would be untraceable to a specific computer once the I.P. addresses are deleted.

Meanwhile, Yahoo has gone even further, and has agreed to delete I.P. addresses after ninety days. In September 2008, Google promised to anonymize (but not delete) its server logs after nine month, but has yet to comply with the six-month duration request. Previously, Google retained user-data for a period of eighteen to twenty-four months.

Sources:
http://www.nytimes.com/2010/01/20/technology/companies/20search.html
http://www.betanews.com/article/Bing-may-beat-Google-to-compliance-with-EU-anonymization-directive/1263933939