Here's a few..
Hot yoga will detox your body via sweating (impossible, kidneys and liver work 24/7 removing toxins from our bodies, sweat is ineffective at doing this).
Certain yoga positions "massage internal organs" and improve organ function (impossible. Seriously, come on now!)
Yoga makes muscles long and slender (impossible, the length of a muscle between it's attachments does not change with stretching, nor will a muscle become more narrow.)
Yoga increases your fitness (very mild increase in fitness if you're unfit to begin with, about the same as from a walking pace. If you're already fit, yoga doesn't drive the cardiorespiratory system enough to make you more fit than you get from running, cycling, swimming, hockey, volleyball, or pretty much any vigorous activity).
And the big whopper, yoga is gentle and you won't get injured (many people get injured from yoga by pushing too hard, and trying to "go deeper" into senseless poses).
I'm not ultra flexible, but in reality, nobody needs to be. I stretch for about 10 minutes in total over a week. No, those are not yoga pants, those are my long-johns
Here's an article with a long laundry list of injuries and the reasons for them, that occur during yoga;
Yoga not always benign
ABC video on yoga injuries
The most offensive part of how most yoga classes are "taught" (more like preached, yoga is a religion, after all), is that yoga uses tried and true Machiavellian methods and cult indoctrination to convince people they should keep coming. It's the age-old promise of hope delivered with a well practiced smile, a deceiving smile.
Very, very few yoga studio's are not guilty as charged, in my observation.
Watch and see.. now that the initial honeymoon period of the recent yoga fad is waning and losing some of it's halo effect, we will see more and more real facts about yoga coming out. More about the injuries, more about the obviously mythical claims, and more about how misleading yoga really is. My only caveat is that there may be some genuine well intentioned yogis out there who don't lie about toxins etc, and won't try to push you into unrealistic poses. Good luck in finding them.
This moderate amount of flexibility does not require 30 to 90 minute classes 3-5 times per week. Just a few minutes every other day or so. BTW, it was easy for me to go out in my back yard in -12C weather and strike this pose. So much for the "need" for hot yoga
Here's an article I've done previously on yoga, which breaks down the most common phoney claims that are propagated by yoga.
Click on the link below to learn about phoney detox claims, how yoga isn't as "hard" as many think it is, and about research that shows it's fairly useless for fitness, has no advantage over simply stretching, and, say it ain't so, is NOT the be-all and end-all for stress management or a peaceful mind..
Is yoga the only exercise you need?