Well, the cost initially was certainly a drawback for me. I got over that.
Otherwise, the biggest drawback of this mat for me is that at 5 pounds, it's significantly heavier and more bulky than the PVC mats, so it's not a great travel mat for those who want to travel light. When I go out of town for yoga workshops I take one of my old, light-weight PVC mats. And that way if the mat gets lost or "borrowed", I don't lose my favorite mat. (Better to re-use my old mats rather than throw them away!)
I've heard that people who practice vinyasa-style yoga can't slide their feet easily on the Jade mat when transitioning from Chaturanga dandasana (plank pose) to Urdhva mukha svanasana (upward facing dog pose). That's true -- I can't roll easily to the top of my feet from plank to upward dog pose, but that's not a concern of mine since usually I don't do a vinyasa practice (I practice Iyengar yoga).
Apparently the Manduka Eko mat has enough slip to make this transition easier.
I've also read that the Jade mat gets too stretchy for some people after a hot yoga workout. But I've never had that problem. (Update -- after three years, it does indeed stretch and it is now time to replace it.)
Exposure to heat and sunlight will degrade the yoga mat. A friend of mine says hers has started to show more signs of wear than mine, since she keeps hers in her car in between classes, and the excessive heat during the summer hasn't been good for it.
For me, the benefits of this mat far outweigh any drawbacks. Take a look at it yourself, and I bet you'll love this mat too!