Usability 
Microsoft unveiled a new search engine Bing, in June of 2009 with considerable fanfare. Search relevance is good and a new related search feature works well. Local searches like " Sushi near 94102" return click to call numbers, photos and maps. It's one of the best ways to find nearby shops and attractions with your phone. There are separate news and image searches.
Unfortunately, Bing seems to be almost completely unaware of the existence of mobile optimized web sites. Mobile sites are getting indexed and do occasionally occur in the results, usually buried a page or two down. But they aren't consistently flagged as mobile
In contrast Google's mobile searches are much more mobile aware with the option to filter results to mobile web only on basic devices.