OK so I love cities at night, I love the reflections, the light and colour and of course the ambience of the whole experience.
However strutting around London with a D300 and tripod is not the safest thing to do so if you plan on doing this take a friend, keep a good eye out especially in the shadows, and be reasonably quick. The longer you and your favourite toy are stood out on the streets the nearer you are to being mugged!
In short, take reasonable precautions and don't enter into conversation with folk, keep safe.
Nikon D300 + 17-55mm 1:2.8 Nikkor mounted on a Manfrotto tripod.