Last fall I took a few months of Yoga class. It was beginners yoga, which does not resemble the yoga I see in magazines. Our teacher was an older lady and she taught us how to move a little to stretch a lot. In most cases we were stretching muscles that never get stretched. It felt really good and improved my posture a bit too. We started doing some of the poses with names and I discovered that even though I am not very flexible, I could do most of the easy ones. I am sure that my hamstrings are about 2 inches shorter than they should be!!
The benefits from yoga once a week were a calmer mind, more relaxed body in general and healthier muscles. When combined with running, the yoga is an excellent way to keep muscles supple and helps prevent some injuries. I highly recommend that if you are an runner, or lift weights, that you take a yoga class and stretch all those muscles you are building up. It will make you feel fantastic physically and mentally.