I dont like them much. At the typical defensive shooting ranges of 10m and in, a draw and double tap to centermass should be instinctive and more of a point and shoot case. I would think that trying to find the laser dot and walk it onto the target would be slower.
The case could be made that if you have a laser sight you wouldnt need night-sights, I suppose.
I don't own any laser-equipped handguns, but...
Polecat, you make a couple good points in support of learning to shoot with iron sights, i.e., learn and master the basics. Most instructors will tell you that you are only hurting yourself if you come to rely only on the laser. IMO, the laser is more of a backup system, for times when you might not be able to acquire a decent sight picture, like laying on the ground and firing from behind cover. And like you said, in poor light...where aging eyes such as mine have a hard time seeing the sights.