I hope it works good on my 8600m GT.
Assume you have a 2.0 GHz Core 2 Duo. Each core can do 4 floating point operations (FLOP) per clock tick. 4 x 2.0 Ghz = 8 Giga FLOPS. With two cores, you're looking at a maximum performance of 16 Giga FLOPS. Assuming SSE optimised code, this doubles to 32 Giga FLOPS maximum theoritical performance.
In contrast, your 8600M GT has 32 stream processors and produces a theoretical 91.2 Giga FLOPS.
Even though these are peak performance numbers, which means you'll rarely ever see them unless you're running specialized software on specialized datasets, you're still looking at potentially 3x better performance by offloading image processing tasks to your GPU.
Just for kicks, I looked up the GeForce 9800 GTX+ and that does 705 (!!) Giga FLOPS