oh, it doesn't act like that on Team Fortress 2. My usage for that is only around 20% and very stable.
however, I ran the GPU monitor on my brother's laptop and the usage was around 50% in the main menu screen. I'm not sure if this is a common thing, perhaps D3 just needs alot of resources to run, coupled with maybe the fact that some of us play D3 for hours on end and that really stresses the card..?
It starts doing this after about 1 minute after I boot the game up.