I have mixed feelings on them, I got to try a pair out the other day and they were pretty slick.
I tend to look at it like this, I wouldn't mind having them especially if I had to shoot from non-standard shooting position where point shooting or sighted fire was a no-go.
I also found a pretty good article on the matter that was worth the read.
Looking at lasers: Myth and-Reality
Even if I had them, I would still spend most of my range time using sighted fire / point shooting only using the laser sparingly unless I was totally wowed by them.
I don't think they are a gimmic and as we all get older our eyesight WILL degrade if even a little making them a very attractive option for some.