In a study published last month:
"... researchers examined how people’s daily activity patterns changed after they began using the sit-stand desks. And they did change. Before receiving the new desks, most of the workers had spent about 10 hours each day in a chair either at the office or at home and less than five hours standing up."
"... and after three months, their daily standing time had fallen to about 5.5 hours and their sitting time had climbed back to a little over nine hours."
"... while the workers were sitting less at the office, they were spending more time seated at home than they had been at the start of the experiment."
"For now, ... the message of this experiment is that someone wishing to sit less should “consciously think” about his or her behavior throughout the day, especially away from the office."
Source: NYTimes Well Blog