Well there definitily is certain evidence like the study I mentioned above. So some of the effects are examined pretty good. In germany the health insurance refunds parts of the expences when you visit a yoga course. So they have accepted the evidence and put yoga on the list of possible prevention courses.
And about my own experience with yoga: the feeling espacially after I did yoga is really extraordinary. So I'd say, yes it works, even if not all aspects are researched yet.