While the search engine may have meant well, what they did on Twitter came across as a tasteless attempt to promote their brand.
As Valleywag points out, "Not how it works, Microsoft: You do something good, then you get good publicity from it. At least pretend to give a s*** about the human suffering in Japan irrespective of the chance it gives you to promote your search engine."
Some people played along and retweeted, but many were outraged and spouted things we cannot repost here, including the hashtag used with the angry tweets. Let's just say there was an "F" and a "youbing" in the tag.
On the upside, Bing has apologized saying, "We apologize the tweet was negatively perceived. Intent was to provide an easy way for people to help Japan. We have donated $100K."