I feel like search queries can be divided broadly into two categories: general and specific. General queries are things like "what is python" or "java tutorial". These are subjects that are well known and have a lot of relevant information on the web. Specific queries are queries things that you and maybe a few hundred people in the world have ever encountered. Think: really esoteric programming erors.
What I believe - and I don't have any hard facts to back it up past my own experience, so feel free to take this with a grain of salt - is that Bing excels in the first category but not the second.
The other day I was doing some schoolwork involving SSL, where I had to write a man in the middle proxy. I ran into this really bizarre error message: "valid not before not set." I had no idea what it meant, and since I was using a proxy SSL server for the assignment I ended up using bing to search for it - no results. Google has exactly 1 result for that phrase, but it's the one that you need to get back on track.
This happened often throughout the project. Bing gives pretty good results; I certainly don't wish to disparage the website. But whenever I started running into really esoteric or weird bugs, Google turned up the right page time and time again. Bing felt like it was taking a hazy guess at the right answer.
These are the specific queries, and this is where Google stays ahead. I've used Bing in the past for a month or two; I've also used duckduckgo. Both are very good. I certainly don't consider myself anything of a google fanboy, for that matter. But when it comes to specific queries, I still can't find a search engine that holds a candle to Google.