Many bloggers have written about the need for the Liberals to "get smart" on crime as opposed to the Tories populist but tax dollar wasting and ineffective polices on crime. The decriminalization of sex work (as opposed to legalization, which would treat sex work as a vice to be regulated, and not simply work) would be a good start. As others have said, simply parroting the Tories on crime does no benefit to the Liberals, both practically and politically, as all it results in is bad policies becoming law, and it doesn't help us politically, as the Tories will still drone on on how the Liberals are soft on crime, and voters won't support the Liberals over the Tories for supporting Tory policies.
The Liberals need to develop some policy backbone on social issues, and not be afraid to fight to Tories on the crime issue. The greatest advantage of having Ignatieff as leader is that we have a leader who has a grasp of complex issues, and has an international perspective. The decriminalization of sex work is a policy that would play to these needs and advantages. Ignatieff can rightly say that countries which have decriminalized sex work have seen a drop in violence and crime against sex workers, and by freeing up our hardworking law enforcement officials from simply being a morality squad, they can focus on real crimes and real criminals, similarly to arguments in favour of the decriminalization of marijuana (which is another issue the Liberals need to be more vocal on). Canadians will always associate the Conservatives with being "tough on crime", so we need to sell something different from the Conservatives, get some clear blue water between us on the Conservatives on social policy issues. Calling for the decriminalization of sex work, marijuana, and voting against the proposed random DUI tests would be a good start.