One thing that annoyed me recently about Bing is that it doesn't do conversions like 6.3 litres/100km to mpg
Google converts that for me right away.
Otherwise it seems to be pretty good. The image and video search is certainly very nice because it doesn't care what country you're in like some other features.
Yes, conversions are a little more limited in Bing than in Google. I never figured out how to convert surfaces and volumes either (m2 and m3 to ft2 and ft3 respectively). But that takes me again in the direction of Wolfram Alpha.