• Despite all the hype yoga is getting, it is not going to take yoga beyond a certain threshold. The kind of business opportunity (travel, apparel, props, studios, books, videos, etc.) shows that it's sustainable across a variety of business lines.
• Yoga techniques have crept into the fitness arena gradually over several decades -- most of the stretches used in competitive sports training are adapted from yoga or Pilates. Familiarity makes a posture seem less alien than it might have appeared 20 years ago. I see this all the time at my gym -- people doing their stretches, which are really yoga poses.
• There's been lots of anecdotal reports about yoga helping people. These reports become word-of-mouth marketing for yoga in far-reaching places.
• Most exercise (weightlifting, jogging) is like hitting the body with a sledgehammer. Yoga treats the body gently and allows for restorative poses within its routines. Yet yoga is a lot tougher than most people think because it requires strength and endurance to get through a 60-90 minutes session.
• You're getting more than muscles and sweat with yoga, especially if you are defining yoga in the broadest terms -- preparation, pranayama, meditation, self-discovery, re-examination of life choices. It's more about changing your lifestyle than burning carbs. At my age, I am reexamining a lot of issues, and yoga provides a broad, useful framework and tools for assessing how I live my life.
• What I don't like is the mixture with flaky New Age mumbo-jumbo. I don't want have to believe in astrology or convert to vegatarianism.

I think there are a lot of other ways of looking at yoga's surge of interest. I don't mean to venture into pop psychology because I don't have any empirical evidence to work from. More to follow.