I play fretless about 90% of the time and read music for nearly 100% of the gigs I do. Yea, I look. So what? But, it should be stated that muscle memory, periphial vision, and ears all work for the times when the notes are coming at you so fast you can't look. Its a combination of things. Basically, I try not to look if it means I'll lose my place on the page, and I'll look if it means I'll be closer in tune. Whatever helps make the best music.