I have a Sig GSR w/novaks, and just sitting in the den dry-firing, or at a dimly lit rangethey are nifty.
As for a real life defensive situation, I think most of us would fall into the spray-and-pray mode. If you're in a situation where you would actually USE the night sights, you probably don't need to shoot to begin with. (defensive vs offensive shoot)
The only counter to that would be maybe a shot across a room at an intruder, but that's on the far side of probability, and you probably wouldn't NEED or be concentrating on the night sights all that much even then.
Frankly, I think they're cool but not a necessity.