So I was writing a simple 2D game with OpenGL and SDL and had this problem when there was awful tearing when running in windowed mode (even though I explicitly asked SDL_SetVideoMode to use double buffering). Didn't worry about it all too much because most of the time the game grabs the entire screen, windowed mode is just for debugging.
Anyway, yesterday I updated my nVidia drivers and tearing disappeared, the game runs smooth and looks nice in windowed mode too. I can see how the problem may be in the graphics driver, but this leads to a question.
Obviously, professional game developers have to deal with a lot of different hardware/software configurations. What are the techniques they use to make sure the game looks the roughly the same on different graphics cards or even the same model of graphics card, but with different driver versions?