I can shed some light on this, as I compared the Targus Chillmat and the Antec Notebook Cooler before I settled on the Targus Chillmat. I was looking for a notebook cooler for my Intel HP laptop, as it got pretty warm after gaming. The Antec apparently has issues with noisy and faulty fans, while the Targus proved to be about 95% reliable as far as performance and reliability (based on user reviews and such). Also the reason I stayed away from the Antec is because a friend of mine had one, and he's on his 3rd one after the first two exhibited different fan issues (one stopped working after a couple of weeks while another one had noise issues).
I've been using my Targus about 1.5 years and its still going strong. I clean it once a month using compressed air to get all the dust out, and it works like a charm. Temperature readings below:
Mac OSX - under normal use/load such as web browsing, Adium, etc. [~45C]
- more intensive apps such as Photoshop etc. [~55C]
Windows XP - since I use XP via Bootcamp for gaming only
- Counter-Strike 1440x900 @ Max Settings @ 60fps [~55C]
- Oblivion 1440x900 @ High Settings [~65C]
Hope this helps.