Personally, I don't like working 12's. One would think that if I only work three days a week I would have more time to do other things. That's just not true. My 12 hour days are totally shot...meaning all I do is work, come home, and go to sleep. If I worked 8 hour shifts, I would be able to do something after work.
Plus, on my days off I am so tired I can hardly function.
Also, when I have to work overtime it usually ends up being 13, 14, or 15 hours.
Personally, I don't think the human body is designed to work for 12 hours straight. Not mine anyway. But, I have a good paying job, so I put up with the 12 hour shifts.