Double the Precision, 1/8th the Performance
Another major feature of the GT200 GPU and cards based on it is support for hardware double precision floating point operations. Double precision FP operations are 64-bits wide vs. 32-bit for single precision FP operations.
Now the 240 SPs in GT200 are single-precision only, they simply can't accept 64-bit operations at all. In order to add hardware level double precision NVIDIA actually includes one double precision unit per shading multiprocessor, for a total of 30 double precision units across the entire chip.
The ratio of double precision to single precision hardware in GT200 is ridiculously low, to the point that it's mostly useless for graphics rasterization. It is however, useful for scientific computing and other GPGPU applications.
It's unlikely that 3D games will make use of double precision FP extensively, especially given that 8-bit integer and 16-bit floating point are still used in many shader programs today. If anything, we'll see the use of DP FP operations in geometry and vertex operations first, before we ever need that sort of precision for color - much like how the transition to single precision FP started first in vertex shaders before eventually gaining support throughout the 3D pipeline.