rFactor had a problem with GeForce that caused a 5-10 second stall, and then game recovered with messed-up textures.
A real killer for league racing, that's why I use DX9 in all training sessions and offline, but I switch to DX8 for league races (wouldn't like to ruin other people's race). I've seen people saying that they also had this problem with DX8, but in most cases the probability seems very low.
My guess is that this has something to do with texture memory size and size of loaded textures.
Seems it occurs on 32-bit drivers only. Windows Vista and Windows 7 seem to be free of this problem, but many people are still using Windows XP 32-bit, including me.
Assuming RF2 won't have that problem, I won't look back at DX8 anymore.
I don't know if it's a bug in the driver or rFactor itself. I had to bypass some GeForce and Radeon driver bugs in my OpenGL applications, too.