Here's a link explaining them. Apparently, they are fairly effective for cooling graphics cards. A lot of people using the Zalman heatpipe cooler for graphics cards have said it does a really good job of keeping their card cool.
I bought mine b/c I couldn't stand the noise from stock cooler. Installation is easy,but took longer than I expected. It's hard applying so much AS3
But yeah, it's great. Only thing is, even though I made sure to tighten all the screws, the plates move a tiny bit if i push it.
btw, my videocard is at 315mhz no problem(stock is 250), around the same overclock I had on my old stock cooler.
oh yeah, me having a cheap generic case is also biting me in the butt. Because the Zalman takes up the pci space below it, I don't have room for another PCI slot because of my pump Gotta find a way to fit a tv tuner card in there....