In the theory of plate tectonics, the earth's crust is broken into plates that move around relative to each other. As a result of this movement, three types of plate boundaries are formed: divergent, convergent, and transform boundaries.
Graphics card temperatures typically range from 30c to 40c at idle and from 60c to 85c under load. Most high end video cards typically have a maximum temperature between 95c 105C, at which point the system will shut off to prevent damage. A video card is not considered to be overheating until it exceeds 90c under load. At this point, artifacting may start to occur up to the point of thermal shutdown.
It depends on the chipset you're talking about. Generally newer cards can go up to about 80 degrees celcius and remain safe. I'd say anything 70 degrees or below and you're fine. Oh and you're perfectly fine with your temperature dropping when you're out of the game. That's a good thing really since the graphics card isn't rendering anything to the display whilst you're tabbed out.