I think California has abondoned plans for speed cameras (for now), but we have have a growing number of red light cameras. I've heard that the disputes are clogging up the system. As Jerry mentioned, these things are operated by third party companies, so there are potential confilict of interest issues.
From Wikipedia (
http://en.wikipedia.org/wiki/Speed_camera):
"One issue is the potential conflict of interest when private contractors are paid a commission based on the number of tickets they are able to issue. Pictures from the San Diego red light camera systems were ruled inadmissible as court evidence in September 2001.[16] The judge said that the "total lack of oversight" and "method of compensation" made evidence from the cameras "so untrustworthy and unreliable that it should not be admitted".