Here is a link to one attack this year, and a search will find a number of others, in Arizona, Canada, Alaska. http://www.huffingtonpost.com/2012/0...n_1891308.html
Right before my trip this year I heard on the news a story about a sow killing one man and her cubs attacking two other campers, all in thier tents I believe. Turns out this happened in 2010, and the bears were captured later and euthenized. Nevertheless, it's unsettling, and there are stories about increased bear attacks in Yellowstone. I'm not particularly worried about something like this while in a campground during the day, but I will readily admit to being worried while sleeping in my tent. Predatory attacks are still unusual, but they do happen. Get over it is the best advice I can give myself.