The camera manufacturers' engineers have greater knowledge of noise generated by their cameras at different settings and how to separate the noise from the true image data, as compared to Adobe engineers trying to reverse engineer noise or lens aberrations after the fact for every camera in production. Only exception is the Canon 5D where the RAW NR is excessive and results in plastic skin tonality.

I have found that when dealing with noise reduction that the Ninja Noise reduction system, which is a part of Bibble Labs BibblePro Camera Raw processing software, does an excellent job of minimizing noise to the point where it seems to completely disappear - I use it on every shot I do, regardless of the ISO and am extremely happy with the results.

I use a Nikon D200 and have not found high noise levels at ISO 400 or below, which covers 90% of my shooting. The few shots above 400 did not have excessive noise.

I use Noiseware Pro if needed.

Some noise is acceptable, but not much, I prefer to fix noise layer if need be.

I find it annoying having to wait the same amount of exposure time just for noise reduction. This becomes very lengthy if you are doing low light 30+ sec exposures and you may miss a good shot on moving images (e.g., lava from a volcano). I found that NeatImage does a much better job at reducing high ISO noise than the camera does and I have control over how much is applied. I set my in-camera NR to OFF and apply noise reduction after the fact, as needed.