Maybe I am just not used to newer technology, but is 50 degree's celcius hot for a 7800GTX? It seems pretty hot for a graphics card.
Is it reaching 50c when you are playing games, or when you are on the desktop? It won't burn at 50c, but it could reach unreasonable heats once you start playing games or use graphical intensive programs. If on the other hand your card is at 50c after playing games for a few hours, i'd say your cooling is quite good. But anyways, you should start worrying once it gets at 80c or higher. I'd say today's card are cooler than older ones, I remember my old 9600xt used to stay at 85-90 celsius on stock settings. Overclocking it by a mere mhz of core just crashed the whole pc.
The high temperature your getting shouldn't be of concern, since the chipsets can operate up to 115°C without risk or damage to the card. The card will operate at 50°C in idle state and will rise up to 74°C at full load.
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My 9800xt is sitting at 72Celsius according to monitor :O But I have had it for 2 years still fine.
My old 6800GT idled at 59C with upgraded cooling. Before, it was 63C idle, 85C load. You're fine.... you have some headroom too.