Check out the technical docs area on their website (link at top of my original post).
The thermabases seem to do an extremely excellent job. They use thin copper as the 'envelope' with a sintered copper wick inside coating. The heat loads they handle are as high as 100's of watts, and they make an isothermal space: that is the water vapor cycle conducts heat something like 4000 times better than copper, so the entire outer surface goes to the same temp almost instantly, including the entire bottom of the heatsink attached on the 'other side' (I would have said 'on top' but they work on the side too). Basically even copper and silver are way higher heat resistances at any thickness than a system like this, which is the biggest limitation to enlarging a solid metal heatsink base to improve cooling: you just can't get heat very far through metal without it building up at the starting point and forming a hot spot. Then when they bond thin copper fins right on top of the upper side of the housing, you have the very smallest amount of metal possible: the small layer on the bottom of the envelope + the small layer on top of the envelope + the fin bases, say a total of maybe 3mm. Can you imagine how badly a large (say 80*80mm spreader plate would perform at 3mm thick? Definitely hot spot deluxe. Basically these thermabases will move heat from say 1sqcm (CPU die) to say 64sqcm (fin base) in about 3mm of metal resitance.
All this also adds up to allowing multiple heat sources on one big heat sink, and they are all locked in at almost exactly the same temp. If you did a GPU and a MOBO chipset along with the CPU (would be a neat MOBO IHMO), the two lower power chips would actually act as heatsinks to the MOBO for the CPU. They also say the bottom can be designed (it's stamped then machined) to accomodate mutiple components at different contact hights. In high power applications they use this to cool several high power components with one fan, but have the temps matched for even performance balance in a circuit. They also use them especially for way off-center heat sources (like right at one edge or corner) where normal heatsinks badly loose it.
Final detail: they can put in through holes for mounting. They would be light anyways, but it would work great on an AMD platform done like that.
I WANT TWO !!!
Consider me signed up, for 2. I nominate Mike to ask them, since he is already on their stupid ignore list. Just joking Mike:)
But if you do ask, see if they just happen to have ones with the satandard AMD through-hole pattern
Aside: I could dream really big and imagine a thermabase case side, insulated inside, with a BIGASS heatpipe onto the CPU. Can you say passive cooling? But I haven't forgotten qokked's sig.