A couple of places around here (Seattle area) have a few. One city gave serious consideration to turning theirs off because so many people were disputing tickets and winning. The courts were getting clogged up and it ended up costing money.
Edited to add, at least here you can request a hearing and request that the guy who understands the mechanics of the system and reviews the cases show up in court. More than a few people have gotten off because he didn't show. One math prof got an automated speeding ticket and beat the system by measuring the distance his car traveled between the camera shots and proving he wasn't speeding.