How come the slider isn't always available? Do I have to have done something before to make the NR slider work?

TIA!

I was curious too, and found this on the lightroomqueen site.

Luminance noise reduction (new process) is disabled for the beta but will be back in the final release.

and from Adobe's site:
http://blogs.adobe.com/lightroomjournal/2009/10/lightroom_3_beta_now_available.html

Image Quality
Sharpening and Noise Reduction
In the Develop module we've focused on tuning our raw processing algorithms to extract incredible detail and quality from your images. Capture sharpening and Color Noise Reduction improvements work together to give you incredible noise reduction results without losing that fine detail. We're only halfway through our noise reduction efforts but believe that you will be very pleased with the results so far. We've actually disabled the previous Luminance Noise Reduction so that you can focus on evaluating the Color Noise reduction implementation.

Thanks for sharing that Tim!!! I was wondering if I had to move a slider somewhere else before I could get that one to turn on! !