I have one and am in the process of putting it all together. Considering the amount of copper involved and the impressive build quality of the block I don't think the price is unreasonable. Put it this way, I got the 6800GT and the waterblock for far less than a 6800Ultra (which I couldn't get hold of for love or money) and expect to be running at the same sort of speeds when done.
Edit: I've now completed the PC. Results and pics
HERE