I have a similar slot fan too. I've read several reviews on that type of slot fan and while they actually do help exhaust heat out of your case, especially handy if they are next to the vid card, however, the general opinion is that someone was high on drugs when they rated the CFM on those fans. They really only flow a fraction of the stated CFM.
nice blowers for helping to cool a video card or a NIC. but the specs i always see rated at 30 and 40 cfm and so on are totally bogus. it's possible those specs are correct, without the fan in the housing, but it's more like 8-15 or so. pretty decent for lightduty spotcooling tho
Here's one another: http://www.titan-cd.com/004_n.htm
I had their previous model, which used a centrifugal fan instead of an axial one. I don't remember its specs, but it was quiet and pushed a lot of air for its size. Wasn't very much either, about $10... I gave it away to a friend for free, but he insisted on buying me a pack of cigarettes