Burberry is great example of using social media to completely revitalize the business. The stock as grown over 300% since 2007. One can attribute their success to a variety of factors but an important prong was social media. I think the difference with Burberry's strategy and say Pepsi's is using social media to enhance the key values/identify of the business.
The site (for now) caters too much to those who already have a set routine. I would develop standard plans that users can pivot from. (Those standard plans should based at minimum on gender, weight, and current fitness to be usable.)
Personally, I would love to use something like this since I find myself floundering at the gym and picking random exercises when I am not on the treadmill. But as a woman, I don't want a suggested routine of 100 x 50 lb bicep curls.
The gaming potential of this is obviously awesome; however, I think this could revolutionize the home good ecommerce world. A user could build an entire room with a couple of clicks.