That is sort of what my line of work is about when it comes to cosmetic dentistry. A veneer is a whitened (porcelain or composite) thin facing that covers the front side of a tooth. They are used to cover up stains that won't leave through bleaching or discolored teeth...or just used to change the shape of the teeth without the use of braces.
It is much like a crown in that any risks of it are usually associated with how the patient cares for their teeth. If you get new veneers and walk out and bite full force into a jawbreaker, you can't blame the dentist if it breaks.
You may experience tooth sensitivity if tooth structure needs to be removed in order to change the shape of the tooth....or even a root canal if the tooth needs to be changed drastically and the shape will encroach on the pulp of the tooth (we are assuming we are discussing someone without cavities on the teeth already).
As far as how much it costs, you need to call whatever clinic you are going to. This is much like plastic surgery in that sense.
I am limiting my response to this because most of the people here don't respect the access they get anyway.