The Targus Chillhub is is designed to keep notebooks cooler. Temperature is an important factor in terms of the lifetime of computer hardware. Also, poorly ventilated systems and surroundings can cause system instability, crashes, or hardware failure.
The Chillhub is sized just right for 15" laptops. That said, smaller or larger ones will work fine with it and I use my 17" widescreen with it all the time. It functions as both a cooler as well as a 4-port USB hub. There are two fans that blow air downward, away from the base of your laptop, and out the back. The fans, and USB hub, are powered either by the included AC adapter or by the USB connection to your computer. Not being forced to use the AC adapter is a nice plus as it cuts down on the number of cord, and power-strip real estate. However, if you have a MP3 player that charges via USB and don't have your laptop hooked up to the hub, you can use the AC adapter to charge it up, so that is also a benefit.
The Chillhub adds about 1/2" to a laptop setup, which I thought would be distracting at first, but it really isn't. Using software to check the various temperatures of devices in my computer, I noticed that with the Chillhub attached the hard drive and CPU were usually 3-5 degrees (celcius) cooler, but my GPU (graphics card) was 10 degrees cooler. Everything here is USB 2.0 and I've not had any problems with device functionality.
Because it's a USB hub and you have to power it (either by AC or USB), the entire thing becomes a bit too bulky to use on your lap, so you'll almost always want to leave the Chillhub on your desk like a docking station. If you want something for portable use you can get cooling mats that are designed to be attached to your laptop all the time, but for desktop use the Chillhub is a nice product.