Are you talking about the squirell cage fan that attaches to the mosfet part of the heatpipe?
My M2N32-SLi Deluxe has one of those (there are 2 places to mount, but only one fan) although I have never used it.
I have noticed that my southbridge was getting hot to the point of burning you if you held your finger there long enough, but I can likely attribute that to the fact that my
mobo was laying flat on a testbench thus nullifying at least part of the heatpipe's effect.
So I spent the afternoon putting my rig back into a case so I could potentially get batter gains on a
RAM review I am working on.