I just filled out a recommendation form that asked me to rate a student's "humility." Every other attribute I was asked to evaluate - e.g. "Intellectual Ability" and "Integrity" - was positive, so apparently humility is supposed to be positive as well. But what's so great about humility?
I'm very much in favor of accurate self-perception. But humility and accurate self-perception are hardly the same. If Einstein said, "I'm only average in physics," he'd be humble, but deluded. On the other hand, you can be humble but still overrate yourself. Think of the saying that "He is a very humble person who has a lot to be humble about."
Well, maybe humble people are just easier to work with? It depends on the kind of work. If your job is just to follow orders, humility is a big plus. But what if you need to work independently, or even competitively? Is it easier to work with a humble lawyer? Maybe if you're his secretary, but not if you're his client.
Now you could say that I'm just rationalizing. People have been complaining about my lack of humility for as long as I can remember. Literally. Nevertheless, at least in the career niche I've found, humility looks like a serious negative. It takes more than a bit of arrogance to think "I've got an important new idea, and I'm going to share it with the world." And if even you don't believe that, why should anyone else?