I've not been impressed with Zalman products in the past, I have to say. They're almost never as silent as everyone claims, since the silence comes at the expense of heat. And even when it's making noise, they still don't seem to cool all that well.
Some of their products have been hit and miss, i agree. Stick with the reviews though and find the gems that really work well.
The Zalman CNPS####X... (dumb long and incomprehensible item labels) copper fin cpu heatsink was a huge contender for best, most quiet HSF for some time. Granted the thing was the size of a Chinese water lily and weighed as much as my dog's lower torso, but one didn't need a high speed fan to dissipate heat.
It was a good design which oddly didn't work so well with some of their other product iterations.
