I would agree with the previous posters that the mounting system is difficult for AM2+ boards. I have an ASUS M3A78T Board (790GX), similar to the one in the installation pics posted earlier in this thread. I got the Kabuto so that I would not have to remove the mobo, but the only way it fits then is by lowering 2 notches on one side of the clip, and 1 on the other. This is not good - there does not seem to be enough contact that way because the temps are quite high - 48.4 C on a non-OC'ed phenom ii 965 C3 at idle, 60 C when running Dragon Age or Left 4 Dead. Thermal Grease is Arctic cooling 5. From the reviews I read (silentpcreview), the temps should be lower.
The issue seems to be that when you are not removing the mobo, in a mid-tower case like the Sonata 2, there is no space between the top of the kabuto and the PSU, which means that your first clip to attach has to be the top one (the one nearest the PSU, in a top-mounted PSU case like the Sonata II). The problem is that when you try attaching the second clip, you end up hitting the northbridge cooler (the same as the one in the pics). This is a bit annoying given that one of the selling points of this cooler is that you don't have to remove the mobo to install it
Anyways, will try with the mobo removed and let you know!