The On-Sight blog has a post titled "5DMk2 - Today's Best Camera For Night Photography". Although you Nikonites may or may not agree with his Canon-centric thesis, there are some very interesting observations about shooting at night with this camera.
(Exposure experiments using ISO6400, photo by On-Sight Blog)
I particularly like his idea for using ISO6400 to work out your exposures before shooting the final image at ISO100 because the ISO6400 "seconds" exposure translates directly into ISO100 "minutes" exposures. For example, 15 seconds at ISO6400 translates to 15 minutes at ISO 100. It seems to obvious. Why didn't I think of that?Thanks to Lance Keimig at TheNightSkye for finding this one.