I was watching a documentary called "Enlighten Up" on instant Netflix the other day. It was an interesting thing to watch, particularly in the second half.
The premise was that a woman who makes documentary films happens to love doing yoga (physical poses, the norm in the west). She wants to see if it has transformative effects on everyone, so she picks a subject, a man with no yoga experience, and has him try out a bunch of different schools.
Interviewing different yoga teachers brings to light that there is a lack of knowledge about the real history of yoga. The different teachers disagree on how old it is and what it means. Some schools are all about the physical aspects, others try to capture a spirituality with it. One scholar argues that yoga as we know it today is only a couple hundred years old (That is, Yoga as it is seen in the West, not its historic path to God, as Dhurga points out in the comments). Another argues that in remote parts of India yogis are seen as sorcerers and have connections to dark magic.
The woman making the film gets really frustrated with her subject, who continues to be unmoved by the spiritual side of yoga. He enjoys the exercise, but remains skeptical that there is anything more to it. Strangely, this makes the film maker angry. So, it's not exactly an unbiased, scientific look.
In the second half they travel to India and after more lack of spiritual understanding, the woman takes him to ashrams to experience "bhakti yoga." Now, this to me was going away from the subject of the film. This is not what people in the west think of as yoga. Yes, in India, yoga means discipline and it covers a very wide variety of activities. Bhakti yoga is devotional worship. It is unrelated to the physical poses of hatha yoga. I think the filmmaker should have stuck with her point.
I've had trouble with yoga in the past. People tend to assume that I'm into it because I do all these "Indian things." Yoga as practiced in the west doesn't seem at all related to Indian spirituality. The teachers who do try to connect it by chanting "Om" a lot do nothing but annoy me. I don't see that physical yoga has any connection to its spiritual origins anymore and it goes back to my lack of trust. I don't want to put my spiritual development in the hands of someone whose only qualification is that she teaches yoga classes.
On the other hand, if I found a teacher who didn't chant during the class, I might really enjoy yoga for the benefits of getting me into better shape and more flexible and resilient in my body.