I did yoga for about a year (about 6 years ago). I never progressed out of the "novice" class, but I was not a hardcore yoga dude like some of the people in class. I liked it mostly for relaxation honestly. I got a little more limber, but this was a very meditative class. Very mellow.
There is a yoga that is vernacularly called "Power Yoga." This style of yoga would be well suited for martial arts. Lot's of balancing power poses (like head / hand stands, one leg stands with the other leg flexed up by your head, etc. and holding tough and ruthless poses for a LONG time). Anyone who can hang with power yoga for 6 months or more is certainly contributing to their own martial arts training.
My advice, from a novice, is to do a little research in your area and find a tough Yoga class, and avoid the "new age" oriented soft style yoga stuff. But... it depends what you're looking for.