2/3?
Are you referring to the proverbial "missing MUL"? (although then the number would be &#189

It's true that in some contexts nVIDIA says G80 is MADD+MUL. Technically it's true but there's a catch. The "missing MUL" isn't even supposed to handle shader instructions - it isn't even part of the shader core.

Infact, the actual shader ALUs appear to be quite efficiently exploitable as B3D found out:
We can push almost every other instruction through the hardware at close to peak rates, with minor bubbles or inefficiencies here and there, but dual issuing that MUL is proving difficult. It turns out that the MUL isn't part of the SP ALU, rather it's serial to the interpolator/SF hardware and comes after it when executing, leaving it (currently) for attribute interpolation and perspective correction.

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...Unlike the SPs on R6 of which only upto 2/3 are utilized even in synthetic tests.