Diversity: Are Quotas Effective?

My colleague, @Laura Ross recently launched Procurious Group 'Bravo' to celebrate and promote women in Procurement. Although it seems reasonably well understood by most businesses that diversity is strongly tied to profitability, many still struggle to achieve better representation at senior levels of the business. For diversity to make a business impact, representation must show at the top, but is that best achieved by setting quotas? Do quotas in fact have a harmful impact if they invite cynicism or reward the wrong behaviours? But is all this outweighed by the simple fact that setting these kinds of targets means what gets measured, gets done? Very interested in your views and how your businesses are approaching diversity targets.