One of the principles we have here at Bing is to constantly experiment and learn. We do this to ensure we are keeping pace with new social and technology trends, and can continue to deliver great value for our customers and advertisers.
As part of this "test-and-learn" mentality, we will be retiring the Bing cashback feature, which means that the last day you can earn cashback will be July 30, 2010.
From the look of the comments, M$ has at least 35 saddened users.
eWeek does a follow-up attempting to explain the situation in more detail.