"Principal scientist" is an important-sounding title, and it's hard to imagine any person holding it wouldn't contribute a lot to his or her company. Unfortunately for Microsoft, it looks like Bing's principal scientist was lured away by Twitter.
Nothing's been confirmed through official channels just yet, but Marshall Kirkpatrick wrote late yesterday with respect to Alek Kolcz, "[W]e noticed tonight that he's been added to the list of staff members on the Twitter website." And that sort of thing probably doesn't happen by accident too often.
So let's consider what sort of employee Kolcz has been and will be. He's held the position of principal scientist for almost two years after spending some time as a scientist for Microsoft Live Labs.
As for what sort of work he's done, Kolcz conducts research in the areas of machine learning, data mining, and information retrieval, according to his LinkedIn profile. His specialties then include spam filtering and content-based personalization, among other things.
It should be interesting to see what Kolcz manages to accomplish for his new employer.