I bought one for myself because I use my computer on top of lots of dusty desks (shops, etc.) So I bought the pad to keep the MBP cleaner. As far as cooling goes, my targus one doesn't do a damned thing. The only time I felt the need to plug it in was during games, and that doesn't really help temps at all. Just buy a lapdesk and you'll be set.
I bought a Targus cooling pad. Didn't really notice a difference in temperature. It's really only useful for keeping your lap from burning. Or keeping your MBP from overheating on surfaces other than flat ones (like desks). Then again, a phone book is cheaper and probably solves this as well.
The first generation of MacBook Pros were *notorious* for running hot -- thermal guns were registering the bar above the function keys at 120'F to the touch.
Anyhow, my experience using the iLap with this generation of MBP that it made a noticeable difference with the MBP being cooler to the touch.
It's not a cooling pad per se, ... it has no fans. However, it is made of aluminum, so the MBP seemed to dissipate the heat right thru the iLap. If you look at how the iLap holds the MPB, I think it'll make more sense.