not sure if there has been a post like this, but I ran across this page today and it gives a good example of images at each ISO on the 300 if anyone is interested!

http://galleries.daveeinsel.com/d300test/

Mine should be here sometime by the end of the week! Yippee

~Courtney

Seems similar to Canon gear. Good to 800, 1600 is decent, 3200 if you must, and faster than that and the flaws take over the photo.
Cory