A dash of color is a good thing and so is the added protection from a hard case—but there are a few drawbacks. Heat buildup might be a major concern, there are no 17-inch versions, and the $50 price tag is a bit steep. [Speck via CNET]
The problem I have with these cases are that they are made of thin plastic that is significantly less durable than the object itself, and more scratch-prone.
The point of a case (to me) is to make the thing either more durable, like a rhino skin, or shock-absorbing, like a silicone case. This does neither, and will scratch and crack faster than than the Macbook itself. Granted, the case takes the damage for a while, but the aluminum housing is just so much stronger than this material.