The number of pixel shader operations that can be performed per second.
NOTE: The way we do this calculation is different for DX9 and DX10 cards to accommodate unified architectures. DX9 cards and DX10 cards are *not* directly comparable based on the specifications we've provided here. To compare DX9 and DX10 cards, rely on benchmarks only.
Pixel shaders are programs that are run on the GPU to add some visual effect to a scene. The number of shader operations per second indicates how quickly the card can perform these operations and, in turn, render a scene.
Newer games are becoming increasingly shader intensive and this number is becoming more and more important.
Though it's not a perfect indicator of performance, all else being equal, a card with more pixel shader processing power will outperform a card with lower pixel shader power. As games get more and more shader dependent, cards with more shading power will pull farther and farther ahead of competing cards.
A perfect example of this phenomenon is the X1800 XT and the X1900 XTX. Both cards have nearly identical specifications, with the exception of shader processing power. The X1900 XTX has 3 times the shader processing power of the X1800 XT. This change alone is enough to make the X1900 XTX nearly twice as fast as the X1800 XT in shader-heavy games.