Once the plans arrive at the fab there are many steps involved in the making of the chip, then testing the chips, then adding them into a card, then testign the card. then shipped back to the R&D lab at NV, testing the cards that passes for clock speeds, voltage requirements, interfereance, etc... a thousand thigns that can go wrong and screw up a good design.
Look at what Intel did with the P4, all the signs pointed for them to keep increasing clock speeds, AMD came though with the more clock efficient Athalon and raped their performance. So they had to go back to the drawing board, found the P3 had the makings with smaller process and tech improvements and with the information about what doesn't work tehy were able to kill the Athalon dynasty in one shot.
NV is in the same spot, as traces get smaller the number of defects per useable area kills yields and useability, lets say for a 280 they had 10% redundancy built in and allowed for recovery of 40% of their yield with defective parts to make a still operational chip. By shrinking the process the physical defect int he chip that used to damage 2% of the chip now damages 4%. A 50% jump in damage, so only two damaged components are allowed per chip, and only in specific areas like the shaders or memory. If they were working with a 10% overbuild, and salvaged 70% of the wafer, and now are facing chips with the same number of defects but with a smaller process they might only be getting a 40-50% yeild from the same wafer.
Either way I await the green camps launch to make my move, unless the 2GB variant hits and is available long enough for me to order.
Just relax man! 
