There are two parts to this understated shield, a top and a bottom, which snap onto a 17-inch MacBook Pro or PowerBook and protect it from scratches and scrapes.
It hugs the Mac so closely that we were concerned about heat. However, vents run all the way along the underside, over the top of the MacBook Pro air vents, and let airflow freely in and out. It worked okay for us - we didn't notice any extra heat problems due to the shell, and it actually protects your lap from excess heat.
On the front of the shell are holes exposing the disk slot, clasp and IR receiver, and all the ports and power point are also exposed. The main advantage of this type of shell is the minimal extra space it needs. It adds very little thickness to the laptop while providing all the scratch protection you could need.