We are currently using UnityIntgration in a Silverlight 4 / .net 4 beta2 project and we have encountered several bugs :
The first one, wich is least critical is that if you register types in your container before calling RegisterCatalog, MEF cannot resolve these registered types.
The second, which if very critical (as complex UI architecture depends highly on it), is that MEF components do not respect ChildContainer Registered Instances.
Here is an exemple of code that fails :
IUnityContainer container = ConfigureMefThenUnity();
var unityComponent = container.Resolve<IUnityComponent>();
container = container.CreateChildContainer();
var component = container.Resolve<IMefDependingOnUnity2>();
Assert.AreEqual(unityComponent, component.UnityComponent); // fails here, MEF is using the rule defined on the parent container instead of the overriden one in the child container
Attached is the full test file highlighting the 2 bugs described above