Mike, My gym offers a twice weekly yoga class and I never miss it if I can help it. Aside from the obvious stress release, I have definitely noticed a huge increase in my flexibility and balance since starting. However, I've taken yoga with good instructors and crappy instructors, and the good ones make all the difference, but then, i guess it is that way with everything.
oh, and i forgot to mention that since starting the new yoga, i find myself working some of the poses into my everyday workout warm ups and cool downs because they're so much more effective stretches.