You may be familiar with the bumper sticker wisdom that "stuff" happens. Or, to borrow a phrase from the cult classic movie Breakfast Club "screws just fall out all the time, the world is an imperfect place." Either way, although we expect sites like Bing and Google to be online 24/7/365, sometimes things go wrong.
Somehow, I actually find it more comforting that it was human error or a configuration flub that took Bing down. Had the outage been the result of usage overwhelming server capacity, or from a malicious attack of some sort my faith in Bing would be more shaken.
That is not to suggest that outages resulting from human error are OK. I expect Microsoft to investigate the root cause and implement some additional change controls to ensure this sort of thing doesn't happen again.
A simple mistake is a tidy problem that is easily addressed and has less impact on my overall opinion of the service. Human error is somehow more acceptable than not being able to survive an attack or handle traffic capacity.