I've been doing yoga since the first of this year. Don't judge by your first experience, as I find that different instructors will significantly change the experience. I'm amazed at the effect it's had on my flexibility. Depending on the approach and the style of yoga, it can be an hour of just really good stretches, or it can be a very challenging routine of continual movement that can provide cardio and/or strength-building elements.

I just started a PiYo class last night - a combination of Pilates and yoga. Had me sweating like a pig within 10 minutes.