I never heard anything bad about them. My brother had a jeep with wheel spacers and nothing ever happened. If you get quality spacers and get them installed properly and with loctite on the lugs and studs, you should be good.
Wheel spacers are excellent for off-road if you also have the large tires. They prevent the inner walls of the tires on the front rubbing up against the chassis when turning thus reducing the wear and tear on expensive tires.