I have been taking Yoga classes at my tennis/fitness center for a few years now. Yoga is wonderful for everything! I'm not a very flexible person, but Yoga has made me more flexible. I don't know how to describe it, but it really is good for the mind & body. The more you do yoga, the more you realize that good concentration is key to performing many of the poses correctly.
With my work & tennis schedule I am only able to go to classes twice a week. But I also practice at home as much as possible. Sometimes I get very busy and skip yoga for about a month and I always feel horrible when I do this. But it doesn't take long to get back to normal with a couple of yoga classes.
Yoga is very complimentary to tennis. It works the core, and helps your balance tremendously. I was amazed at how many more balls I could get to after I started doing yoga. I highly recommend it.