This reading should give you some ideas (perhaps as it explains delays as well as increase in overall R&D cost).
Initially NVIDIA ran into a can of worms with the A1 revision of GF100 (Fermi), yields have had to be incredibly horrible as they very quickly shifted to revision (build) A2 of the ASIC. After revision A2 was out some time passed and TSMC reported that the majority of their 40nm issues had been solved. Good proof of that is that ATI is pushing out many DX11 class products in much diversity and reasonable volume. That means the wafer yields though likely not very good where okay enough. So there's something else going on as well next to yield issues. Either a bug slipped in or the thermal package is causing issues resulting in lower than anticipated clock frequencies and perhaps heat related issues.
We found out (and verified), surprisingly enough, that the GPU is already at revision A3, that's the third revision of the GPU, the GF100 already has had three builds. So yes, something was wrong, very wrong alongside the initial yield issues. But we know that the products right now are in volume production, will it be many weeks before we see good availability ? Sure it will. Maybe April, or indeed May is where things will start to make a difference. Performance will be very good, however with the clocks I have seen (and only if they are final) I do believe they will not be brilliant though. NVIDIA has many trump cards though, they have an outstanding driver team which will drive performance upwards fast and soon.