He left Microsoft to become vice president of development for search for the auction site and, judging by Williams’ LinkedIn profile, eBay gains the guy that helped created Bing:
I was a Partner at Microsoft, and a development manager in the Bing team. I’m proud to say that many of the features of the first Bing release were created by my team.
I managed the development of all user-facing web search relevance features, including the left-rail explore pane (with its "table of contents"), navigational query treatments, query-biased summaries, "deeplinks", related searches, and whole page results relevance. Additionally, I managed the Powerset team in San Francisco.
He also played a key role in Microsoft’s development of Internet Explorer 8.
So, two questions. What damage does this do to Bing, if any? And, what the heck does eBay have up its sleeve?