I'd be curious about the quality of the instructors, especially on the yoga half of the equation. My gut tells me that Spynga is a fad that has attracted some less than well-trained teachers who sacrifice proper form for "a good workout." Of course, the same holds true for the spinning side of the equation. There are a lot of bad instructors out there.

But that's just my gut. I'm willing to keep an open mind about it.