A couple of weeks ago in Bowling Green, there was a night IDPA match. I am not much on IDPA style shooting, but I went because it was an awesome oppurtunity to put in practice all the things that are being debated in this thread. I know it was a "competition", but it was good practice. MCTS, in Dickson, is having another night match coming up. It would be a good oppurtunity to put theory into practice.
I do not have any night sights, but my XDM has a fiber optic front, and when I held the light by my head, and shot strong-hand only, the sight was super easy to see, the when I went with a two-handed light/gun friction hold(I am sure there is a tactical name for it), The sights were a little tougher to pick up, but I shot more accurately, but a little slower.