Definitely no need to worry about black bears. I was sleeping up in Yosemite a few years ago on a beautiful clear night so I hadn't bothered to put the fly on my tent. I woke up at some point to something pushing on the side of my tent. Thinking it was one of the guys I had come up with who was messing with me. I put my glasses on, sat up to the point on my tent where the mesh was transparent, and was face to face from about 1 foot away with a black bear. I just remember us staring at each other, probably for just a few seconds, too scared to move, when it reached down, grabbed my backpack in its mouth, and started to run off.
After the shock wore off and I realized I was probably going to need my pack to hike out I jumped out of the tent and started yelling and chasing it. It finally dropped the pack and ran off.
I learned several lessons from this experience:
1) Black bears are smaller than grizzlies, but they are still big enough to scare you to death in the middle of the night
2) Bears have an amazing sense of smell, strong enough to detect the scent of an electric tooth within a backpack, and apparently the appetite to eat one as well
3) Black bears are not aggressive, or else I would be dead.