I'm not going to pretend I'm an expert on the subject, but I will use this comparison: you wouldn't start your very first Cathe experience by doing power 15s, or Interval Max, for that matter. I think it's safe to say that most of us doing yoga may never get our foot behind our head (but correct me if I'm wrong ;-)). I've seen some yoga books out there and they've scared me silly, too. Fortunately, there are some great tapes and DVDs out there, so you should really give it a try.
The benefits I receive from yoga are primarily flexibility and relaxation, but there are some tapes I do that have given me strength gains as well. I won't even venture into the spiritual part of yoga, but there is that element as well, and maybe someone else out there can help with that.
There is a set of tapes from Yoga Journal (Beginners, Relaxation, Meditation, Energy, Strength and Flexibility) that usually contain two workouts under an hour in length each, and are well-instructed and easy to follow. Based on their titles, each one has a different focus. Living Arts' A.M. and P.M. Yoga (especially P.M.) are 20-minute workouts that leave you feeling as if you just swallowed a spoonful of warm honey--all relaxed and happy! Living Arts' Yoga for Athletes is more of a yoga-infused stretch tape targeted at improving the balance and flexibility of athletes.
Many instructors are incorporating yoga-type moves into their workouts, like Karen Voight's YogaSculpt and Grace Lazenby's All the Right Moves. Both of these tapes use certain poses which build core strength and improve flexibility.
There are so many other yoga tapes out there--I've barely scratched the surface with my list of favorites. Check out the reviews at videofitness.com.