Looking at the last 120 days on our ecommerce site, Google has been losing out slightly to Bing over the past few weeks. It is not a lot - going from approx an 88/12 split to a 86/14 split. That is based on total revenue, not hits. The revenue per visitor though is slightly better with Google.
Bottom line is that we are paying more attention to Bing now, and have also upped our ad budget a small amount on Bing in the past couple of days.