Now I think I heard somewhere (Usually thats not a good way to start a sentance, but...) that even the most powerful of laser pointers or laser aiming devices have something like 5000 seconds of continued exposure to an eye before they begin to produce even negligible damage to the eye. Of course, don't go pointing lasers into people's eyes, to begin with, but that seems like a rather mitigating factor for lasers in general.
As far as lasers go for aiming assistance, I'd have to agree with Paco, they're likely going to be an indoor only type of thing. I myself have never used or owned a laser for use on a weapon, (Airsoft or otherwise) but I would imagine it's not the kind of thing you could use outside during the day with much success. I have a nice red dot sight for my SR-16, and I don't use it much, because I don't see it increasing my accuracy or anything, its purely cosmetic to me. (Which, may be important to certain people) When I first got into airsoft, I thought I might use a laser, because I figured I could see where my bbs were going to land... but I quickly learned that the bbs themselves provide a very decent tracer effect, and thats more than enough for me to correct my aim.
As I said, cosmetically, lasers are cool, but useful, I'm not sure...
Raith