Mark and Chriss - LR3 and ACR use the same engine and I use both. Most of the time there is little or no noise to bother with. On some images, however, I can get an acceptable reduction in noise in either.
The area I have the most problem with is night shots and distant wildlife that has to be cropped and sharpened. It can also be a significant issue with tonemapped output. One could argue that these images are too far gone and should be trashed anyway. At the point I am in my learning curve, and particularly because it is not always possible to do a reshoot, I'm trying to get a feel for how far I can go so I am pushing the envelope so to speak.
In addition, I have some favorite images, like 'After the Rain' (
http://frostbyte.smugmug.com/Photogr...the-Rain-L.jpg) that I would love to find a way to address the significant noise in the sky.