I live in Ontario (Canada) and a friend is an enthusiast. According to his understanding of the current regulations, if you use a UAV for any kind of remuneration, then you have to fulfill some federal flight regulations, i.e., flight plans, proof of insurance, etc. He joined a local flying club and his membership in that club provides him with insurance for personal use. It sounds like the regulations may be in flux, as some of the requirements are more obviously attuned to flying aircraft, not UAVs. Getting insurance is a good idea, you should not assume that you're covered by your home insurance.
Sooner or later, one of these is going to doop out of the sky and injure someone. It may have already happened. Also, sooner or later, we'll have mid-air collisions of UAVs. And yes, people will start shooting down nuisance drones, I am sure of it.
As for photo use, it will probably be a fad for a while, new toy syndrome, but some nice work might emerge. They are already very popular at sporting events, amateur or otherwise, providing coverage that would otherwise be impossible or very expensive to get.