Noise reduction in Lightroom 3 is impressive, but there is no magic number or "right way" when it comes to setting your luminance or color noise reduction. It is all based on feel. Modern cameras have attractive grain structures, so noise reduction isn't imperative, so it really is up to your eye and preference.
All that being said, here is a video with my thoughts on the subject of noise reduction and ISO.
Loading more stuff…
Hmm…it looks like things are taking a while to load. Try again?