OK, ran some tests just now and had some interesting results.

I wanted to stress the system in a way that was similar to 3D games while in a controlled environment. I used Orthos (just Prime95 in a package) to maximize the stress on the CPU and RAM.

I used ATi Tool to maximize the stress on the graphics card (7800GTX) and control clock speeds. I used NVidia NTune for redundancy monitoring of the GPU.

I used Rightmark CPU clock utility and Windows task manager to monitor all aspects of the CPU and bus speed.

Using the 3D View in ATi Tool I was able to get a consistent load on the GPU while monitoring the frame rates of the 3D render in a window. Under default GPU settings (400/1100MHz) it averaged around 300fps. I've attached a picture (1920x1200 resolution) to show the setup and what happened to the frame rates under load.

screenshot

What happenned is a consistent drop of framerates as low as 20fps from 300fps for about one to two seconds occuring every eight seconds. The slowdowns didn't occur immediately but after a couple minutes the fan speeds began to spool up automatically then the problems began to show shortly after that. Increasing the CPU fan speed to maximum (fn-F2) increased the cycle time to about every 11 seconds. Lifting the back of the computer approximately 1.5 inches above the desk to allow better airflow underneath increased the cycle time to approximately 40 seconds. I ran the computer in this configuration for at least ten cycles each time to ensure the results were consistent. You will notice from the screenshot that there is no indication of any drop in CPU or GPU output but that doesn't mean the graphics card isn't throttling, it just doesn't show up on the monitors.

Another test I ran was to underclock the graphics card down to 200/600MHz or approximately half speed. Running the same tests gave me a consistent frame rate of about 100fps and the slowdowns didn't occur at all. The internal fans also never spooled up to maximum.

So clearly I was wrong about this in some respects. It is definitely graphics card temperature related. I'm not sure exactly what's happening to the graphics card to cause this to happen but I may forward this to NVidia and see if they respond.

Something else...I had this same problem on my new 640MB 8800GTS desktop graphics card last year when I bought it but only while playing the game FEAR. I've since bought a new case and built a new system with this same card and the problem has never come back. My new case has much better airflow and stays much cooler but I never tried playing that specific game again and the problem never occurred with any other games.

Since this problem seems to occur on Clevo 570 style notebooks and various NVidia mobile graphics cards it seems to me this is a combination of inadequate cooling on this particular notebook and a fundamental flaw (or a feature designed to save the chip) in the design of Nvidia graphics cards. The reason why it affects some people more than others is simply that all chips don't come off the line created equal, some heat up more than others. But this problem affects enough people that it needs to be addressed.

In the meantime, I would urge caution buying a high end NVidia graphics card in a smaller or slimmer notebook like the 570 without thoroughly testing it before the warranty or return for refund date expires. If you're forced to deal with this issue elevate the notebook, blow a fan across the bottom, or just downclock the GPU a little until the problem goes away.