The GeForce FX was built upon NVIDIA's new, state-of-the-art 0.13-micron process, yet the sheer number of transistors makes it a heavy heat producer. The cooling solution employed by the NV30 has been routinely bashed. Not only did it block a PCI slot, but it was extremely noisy. NVIDIA has promised a lower noise cooling solution for the NV35. However, since rumor has it that the NV35 will feature an additional 5 million transistors, that may be difficult to do. Also, considering how ATI has been able to do more with less, NVIDIA should consider refining their design to use fewer transistors...but have them work more efficiently.
Finally, there is the issue of timing - when will NVIDIA officially announce the NV35? This has to be a very sticky issue for NVIDIA. If they announce the NV35 now, they will doom GeForce FX 5800/5800 Ultra sales (and hurt 5600 sales as well). However, if they don't announce something soon, they risk losing customers to rival ATI.
It's much too early to say that NVIDIA is in trouble. However, if NVIDIA fumbles the NV35 launch like they did with the NV30, they could face an uphill challenge to regain the hearts and minds of the NVIDIA faithful. As NVIDIA's CEO Jen-Hsun Huang said, "We can't make the same mistake twice. When you're in a tough spot, you focus on getting the job done."