The current issue of Justice Quarterly has this great article on recidivism and sex offender registries.  The article's byline, so to speak, is captured in the abstract:

The purpose of this study is to investigate the relationship between failure to register (FTR) as a sex offender and subsequent recidivism (N = 2,970). No significant differences were found between the sexual recidivism rates of those who failed to register and compliant registrants (11% vs. 9%, respectively). There was no significant difference in the proportion of sexual recidivists and nonrecidivists with registration violations (12% vs. 10%, respectively). FTR did not predict sexual recidivism, and survival analyses revealed no significant difference in time to recidivism when comparing those who failed to register (2.9 years) with compliant registrants (2.8 years). Results fail to support the supposition that sexual offenders who fail to register are more sexually dangerous than those who comply with registration requirements. The punitive emphasis on registration enforcement may not be justified and might divert limited resources away from strategies that would better facilitate public protection from sexual violence.

But there's more to the story.