If you are using EMF < 2.9 and the newest CDO you may/will get problems with your Model-Plugin.
The problem is that the current Eclipse PDE won't handle osgi-fragments correctly. CDO uses an osgi-fragment bundle in order to produce a compatibility to EMF < 2.9. In the eclipse/osgi runtime this bundle works perfectly! But inside the Eclipse Workspace while developing, eclipse complains. The PDE "problem" is discussed here: Integrate the new MinimalEStoreEObjectImpl