Yeah, the spiritual aspect is what is unappealing to me. I'm not Hindu (or New Age) and don't want to be subtly pushed into practicing it.
I was just listening to something on NPR about this book,
Hell-Bent: Obsession, Pain, and the Search for Something Like Transcendence in Competitive Yoga: Benjamin Lorr: 9780312672904: Amazon.com: Books , specifically about the narcissistic element of yoga that people don't want to talk about.
Yoga is one of the six āstika ("orthodox") schools of Hindu philosophy.
I'm not sure how you would practice yoga w/o practicing Hinduism. From the goals of yoga to the physical poses, it's all based on spirtualism and worship.
If the instructor is telling me to salute the sun, to worship the eternal presence of Vishnu, to release the flow of my life force and to immerse myself as one with the spirit, it has crossed the line IMO from a physical activity to spiritual practice.