Mine is turned on around 7.30am in the morning, and rarely off before 1am the next morning, every day. I tend to leave it running during the day, but almost always turn it off at night. As others have said, having an SSD really makes start-up time so much faster to a point where its really quite possible to load the OS everytime without any real delays.
Sometimes I leave it running overnight when busy doing other duties, but if I know I'm going to be out of the office for a few hours I'll turn it off during the day as well.