OSHA recommends 68-76°f
Cornell's Human Factors and Ergonomics Laboratory suggests 77°f
The Finns like it cool 70-72°f
Zuckerberg is a crazy person. [He also keeps his office at 59°f] (http://www.theguardian.com/technology/shortcuts/2013/mar/11/facebook-staff-chill-cold-offices)
The researchers at Cornell get my vote
"At 77 degrees Fahrenheit, the workers were keyboarding 100 percent of the time with a 10 percent error rate, but at 68 degrees, their keying rate went down to 54 percent of the time with a 25 percent error rate," Alan Hedge, professor of design and environmental analysis and director of Cornell's Human Factors and Ergonomics Laboratory