I mostly just do yoga and some very light weight training with my tri training. I could probably do more core work, tho, to be honest.
It helps, although a strict weight routine would probably do me even better (I just can't find the time to fit in another hour or two of working out during the week without feeling like I'm overextending myself). I guess I could use that hour a week of yoga and do weights instead, but I really like the stretching that the yoga gives me.