I just downloaded a trial of the FastPictureViewer and am impressed with the results. After instructing it to use my monitor profile (calibrated with an Eye-One Display 2) the NEFs look exactly as they do in View NX 2 and Capture NX 2. And as you've advertised, the load time is MUCH faster, especially with GPU acceleration turned on.
Unfortunately, I didn't have as much luck with native color managed windows 7 applications (photo viewer and photo gallery). Since installing the trial of FastPictureViewer also installed the NEF codecs, I am able to see all my NEF previews in windows explorer, but when I open them with windows photo viewer, the color is desaturated and incorrect.
To test that the right monitor profile was being used, I saved a NEF as two different JPEGs, one with a Nikon Adobe RGB profile, and the other with an sRGB profile. Both of these JPEGs looked the same in windows photo viewer, confirming that the monitor profile and JPEG color profiles are working correctly together. This has me thinking that perhaps the NEF codec is not able to pass the color profile of the NEF through to windows photo viewer, and so it renders it incorrectly. Is this a limitation of the codec, or am I doing something wrong?