From what I understand, Black bears are not anymore dangerous in Yellowstone. Most times, they do in fact bluff charge in attempts to spook or ward off any perceived threats.
Bear attacks on humans are extremely rare occurances, though. For every ONE person attacked by a bear in the U.S. per year, SIXTEEN THOUSAND people are victims of homicide. People are FORTY-SEVEN times more likely to be attacked by a dog than a bear. Human maulings and deaths caused by bears account for barely a fraction of deaths people suffer from bee stings, lightning strikes, dog attacks, homicide, suicide, and car accidents each year.
Unless you've been feeding a Black bear or try to pet a cub (or venture into a huckleberry patch when one is feeding

), they tend to have a natural fear of humans. Their natural reaction is to run up a tree if they see humans. It's the Grizzly bear that is naturally fearless of humans

. They are the largest predators in North America and they know it. They have that "Large and in charge!" mentality

.
I have not heard of any Black bear maulings in Yellowstone this year. There have been several folks like myself who have been bluff charged by a Black bear, but so far nobody has been injured by one.
There was one death in Yellowstone this year, and it involved a Grizzly bear being used for research. Apparently the victim had been warned that there was a tranquilized Grizzly in the area, and yet he still ventured in to get up close and personal with the bear. Not only did it cost him his life (bears are VERY PISSED after they have been tranquilized and relocated

), but also the life of the bear. Due to the stupidity of this individual, the bear had to be euthanized

.
So, if anyone here is interesting in visiting Bear Country, please do respect the bears by not approaching them too closely or feeding them. At least most of our bears have been kept wild with the help of our visitors cooperating with the park on bear safety and regulations

.
I hope I was able to answer your question. Please let me know if further answers are needed or helpful

.