I am also having this issue. I was given a new ASUS X53SD laptop with the Intel HD 3000 integrated graphics and the NVIDIA GeForce 610M graphics card.
The laptop display is hard wired into the Intel graphics card so it can't be disabled without losing the display. No matter what combination of settings I select between the two cards, games will not run properly.
Diablo III has constant screen freezes every few seconds that last three to ten seconds then the game 'speeds up' as if the frames that were frozen are being sent to the display at a faster rate than normal to 'catch up'.
When looking at the NVIDIA PhysX interface in the NVIDIA Control Panel it shows that the Intel graphics are directly connected to the display while the NVIDIA graphics are not. Is it possible that the NVIDIA card has to output the rendered frames to the Intel graphics which sends them to the display? If this is the case, could it be that the NVIDIA graphics are rendering and outputting frames to the Intel graphics faster than the Intel graphics can process and send them to the display?
I've checked that I have the most up-to-date drivers from the ASUS website and I cannot find any way to alleviate the issue when playing games.
Since my original post I have reinstalled Windows 7 along with Service Pack 1 but have disabled the Windows Automatic Updates as I had read on another forum that there is a particular Windows Hotfix which is the cause of all these troubles. Since doing this all reported issues have been resolved. I am not sure which particular Hotfix is the cause and I do not intend to install them one-by-one to find out!
By default the system uses the Integrated Graphics Card (Intel) however you can specify in the NVIDIA Control Panel specific applications to use the NVIDIA driver or you can simply right-click your application/shortcut icon and select "Run with Graphic Processor > High Performance NVIDIA driver" etc.
Regarding Diablo III aparently there is a compatability issue with the current NVIDIA drivers and Diablo III, regardless of what NVIDIA Hardware you have. I believe this should be fixed in the next release of NVIDIA drivers.