While not ideal for most situations, these things could be decent for large, negative-pressure cases where some areas get starved of fresh intake air. My P182 was a good example - CPU temps were ok (at best), but the graphics card temps were horrible. The problem? A relatively low CFM, quiet fan that I placed in the middle rack was the only thing feeding the graphics card any air at all, and even then barely any made it all the way there (most ended up going right out the top exhaust). Then again, a couple of fan shrouds linked together and a relatively high static pressure fan should do the same thing.
It seems that they would be relatively poor for exhaust fans (because who cares where the exhausted air goes, as long as it's out) and not all that useful as heatsink / radiator fans (since the air is already being directed through the fins).