I am running Windows 7 and on both the 2010 and the 2011 Mac Mini I find that the fan kicks in at a higher temperature than under OS X. This makes the situation worse for those running Windows.
Initially I drilled a series of 1/8" holes in the bottom cover plate in the area above the grill surrounding the WiFi antenna. I've have enlarged these now to 11/64" but this makes the placement of some rubber feet critical since the bottom flexes a lot more which was not the case earlier on.
I get the impression that at 2300 rpm the front of the Mac Mini is cooler than at the back. This leads me to believe that the body plays a large part in the (passive part of the) cooling.
The 2010 Mac mini uses approx 8 watts at idle and the 2011 i5-2530M about 15 watts and imho the cooling system is not sufficient enough (at idling at least) for the 2011 mini. Something must be wrong with the fan control as well under BootCamp.
I am now seriously considering adding two heatsinks on the outside of the 2011 Mac Mini ( http://www.aavidthermalloy.com/cgi-bin/exdisp.pl?Pnum=60560&therm=1.36558047469492&airflow=57.2&AirUnits=LFM&CType=Natural&ExLength=30&LengthUnits=mm&SButton1=Change+Length).
I intend fastening one on each side with doublesided adhesive thermal tape. This should aid in channeling away an additional 10 - 15 watts of heat from the body.