Never

I've never bought an Nvidia graphics card, and never will if they maintain that attitude.
They certainly have the right to conceal their Imaginary Property through trade secret rather
than copyright or patent, but the rest of us have the right to not give them our money.

I used to do just fine with cheap graphics based on old chips.  When I finally needed 3D
performance (for the FLOSS FlightGear FlightSim), I got an ATI 9200 based card, the last that
ATI released info on before they went closed.  With AMD opening up the specs, it will be
ATI/AMD for my next upgrade.

(And if I should ever get the need to play closed-source games, I'll get a game console.)