About unlocking pipelines: Most Card Manufacturers will sell a bunch of "defective" 6800Ultra's (the base card) as 6800nu's. I say "defective" because, in the manufacturing process, these cards are less than perfect (I.E., maybe one or two of the pipelines is physically broken...or the GPU just cannot perform stably at 400/1100), but still can perform reliably at the 6800nu level (set by NVidia). So either they lock the broken pipelines, up to 4 of them (if the card has more than 4 broken pipelines, it's pretty much screwed anyway) in the BIOS, or burn them out on the circuit board, write the BIOS as a 6800nu to clock them down, and sell them off as 6800nu's. Also, they do the same to 6800GT's. 6800GT's are most likely 6800U's that "didn't make the cut", so to speak...performed slightly inadequately at Ultra levels, and as such, were clocked down and sold off as GT's. Then this leaves the Ultras as the cream of the crop, filtered and the ones that can perform at Ultra levels extremely reliably. And as such, are sold off as the Ultras.
AFAIK, that's how it's done. Which is why Pipeline unlocking sometimes works; the pipelines aren't "broken", the GPU is simply imperfect...but in other case, the pipelines really are broken.
Anyone more knowledgable care to comment?