Frostytech published a review of the Coolermaster Hyper Z600 Passive Heatsink.

Quote from the review: "The Coolermaster Hyper Z600 heatsink is a novel passive CPU heatsink for today's dual core processors. Its' 'star' shape, widely spaced aluminum fins and prodigious number of silvery copper heatpipes allow it to work without the benefit of a fan, albeit within specific thermal limits. As far as passive cooling goes (and I mean true
passive cooling without any fan blowing toward it) Frostytech threw caution to the wind and stressed the Coolermaster Hyper Z600 heatsink in its passive mode."
Read the full review on Frostytech.