My home is kept at 65 degrees in the winter and I managed to get a constant idle temp of 22-26c with all voltages turned way down and CPU speed at 1.5 Ghz. I also noticed that I see no difference surfing the net or operating my computer (except for gaming) at these low performance profiles. It says a lot for keeping a computer overclocked all the time. Just will heat up the CPU for no good reason for no improvement in 2D performance. This is with a i7 920 processor and an H50 Corsair water cooler. I am a believer about the new intel enhanced speedstep. It boosts up to 3.6 as soon as I put on a game but otherwise keeps the system at 1.5 Ghz.
My cabin gets down right COLD in the winter and I've seen 18-21C (across 4 cores) at stock speeds on my i5-750. It's really all about ambient... I do NOT count on those temps in the summer... and I don't run at stock speeds, but still.