I couldn't agree with Chris Wysopal (CTO, Veracode) more in his recent podcast with O'Reilly Security Podcast where he explains why shifting security to the left (to developers at the start of the development life cycle) is key in an agile environment to keep up the pace and speed.
Security should be made easy for developers by using IDE plug-ins, scanners and educating them to have the basic security skills (hygiene). Organisations should not be solely relying on security experts or a centralised security team who validates all changes. Our typical security modus operandi is broken (call in the expert!) and we need to integrate security into development teams to ensure quality is maintained whilst staying agile.