Eric,
I have read really good things about the Nikon D700 and night photography.
Until quite recently film was the big dog for night photography because of the issues of heat related noise in digital cameras. However, some of the files from the D700, regarding long exposure noise, look almost as good as film.
In this D700 image you will see that noise is moderate but not offensive: http://www.flickr.com/photos/disavage/3239831625/sizes/o/
Again, moderate but not offensive. This is about as good as you can expect with digital: http://www.flickr.com/photos/jnppvch/3046503592/sizes/o/