Should be okay as long as it has good ventilation. You wouldn't want to leave it on a blanket, or something like that which could block the vents. But on a desk or other hard surface I wouldn't expect problems. Even better if you can prop it up a little so there's plenty of clear space beneath it.
Most laptops have thermally controlled cooling. Listen to it run. If the fan cuts on and off that means it's staying cool. If the fan runs continuously that's a sign it's not cooling enough for the fan to cut out.
Should be fine.
Toggle the LCD Screen off and that will turn your graphics processor off too. Much less heat.
http://sitemaker.umich.edu/media.equipdata/video_toggle_keys