Advocates of video surveillance say it has contributed to a long-term decline in other crimes in Britain. Car thieves, in particular, seem deterred by the prevalence of cameras on lampposts. But Dr. Murakami Wood [an expert in video surveillance at Newcastle University] noted the incidence of violent crime actually rose slightly last year.Link
Just as video surveillance does not prevent many crimes, it also apparently has less of an effect on ordinary human behavior than some critics feared it would when Britain began installing the cameras in earnest after a pair of Irish Republican Army bombings in 1993 and 1994.
Original Pittsblog post on "The Pittsburgh Panopticon"