I used to set my thermostat to at my old townhouse to 58-62 deg F in the winter and 70-74 in the summer. The computers were on the second floor. The thermostat was on the ground floor.
It got over 80 degrees in the computer room for most of the summer. I had to turn down my OC's from May through about September.
In the winter it was usually around 65 or so degrees. That made for some nice Overclocking.
Since that time, I've moved. I have a basement now. Even with my Server, HTPC, and 2 PC's (as well as stereo, speakers, TV, 3 CRTs, and 24in LCD), the temperature in the rec room usually stays comfortably below 70. (AC set to 75, around 75 upstairs, upper 60s in the basement.)