The database could be mined to improve answers in Google. When someone asks "what is the best X in Y", Google will know and MS won't. They might have some as-y

The database could be mined to improve answers in Google. When someone asks "what is the best X in Y", Google will know and MS won't. They might have some as-yet-undisclosed IP which one of the big search companies would be able to defend - rather own it than fight it. Also, integrating the already-refined code and ideas into Buzz, Wave, Orkut, other future social initiatives.