The next Zbrush version is heavily focused on the displacement mapping system. There is a large thread on the topicat CGTalk with a lot of renders from the beta. the screenshots in the thread are rendered in PRMan, so I guess that ZBrush itself does not render micropolygons. Uh. And it's not released yet. So the main difference between Poser 5 displacement and ZBrush displacement that I'm using one of them for almost two years by now.