Search on macrumors for my posts: ( primarily http://forums.macrumors.com/showthread.php?t=1210567 )
Drilling the ventilation holes hardly made a difference at lower speed however I am under the impression that it makes a difference at higher speeds. (used to be involved in electronics and have a drill template to create evenly spaced holes)
Since the 2011 has more often higher fan speeds I consider air filtering a welcome addition (see my other posts on this subject). With overhead lighting (ceiling lights) the filter is not even noticeable. Less dirt buildup internally = better cooling. No dismanteling = no warranty invalidation.
I've also a post on references to safe operating temperatures and running this machine above 80C is not advisable, it will impact reliability. ( http://forums.macrumors.com/showthread.php?t=1261199 )
Increasing the idle fan speed to 2200 rpm gives it about the same idle temperature as the 2010 mini. I am only running Windows 7 (I know) and am using MacFan0_65 utility to set the fan speed after startup. Wrote a few *.bat files and have shortcuts on the desktop to set the speed to 1900 / 2100 / 2300 plus one for checking the temperature. Initially I could not live with the 2011 upgrade but now I can (need the improved data throughput from Sandy Bridge)
I love the Mac mini (especially the 2010) since there is no equivalent quiet, same small form factor PC.