As the revenue generating end of Microsoft's online services division, the popular bar chart showing quarterly losses exceeding 600M says that it is a failure. This may turn around if Bing hits its magic number in terms of market share. But one would think that the division will have to have start stemming its tide of losses if it is to be given a chance.
I remember reading somewhere that Microsoft is targeting 2014 as the year that Bing is supposed to stop losing money. I can't seem to find it again though.