Here is a news story about Washington DC ending its mandatory bicycle registration program due to its negative effect on police-public relations. I think the report prepared by the DC Office of Police Complaints is particularly interesting. They find that (1) poorly communicated local bike regulations that are inconsistent with surrounding communities promote public ignorance of the law, (2) impounding offenders' bicycles is an inappropriately severe punishment for the offense, and (3) selective enforcement and pretextual stops create a public relations problem for the police.
From League of American Bicyclists News:
DC Bike Registration to be Eliminated
The Washington, D.C. Police Complaints Board submitted a recommendation to the city's mayor and police chief recommending the elimination of DC's mandatory bike registration law. A number of complaints received by the Board suggest that MPD officers have enforced mandatory bicycle registration in Washington, DC, sporadically and improperly, raising questions about possible bias in these stops. The Board referenced the League's position paper in the report.