Is serialization of parameters and return values required?

Neither seriliaziation or return type are required. Although it is required that parameters were either primitive type or of serializable types (most of Java JDK classes are serializable). It is not important for the current version but in the future parts can be distributed over the network and then the serialization of the messages will be used to send fired events to a remote part.

So, when I pass an object from one part to another, I'm passing a pointer into an address space that both parts share?

I thought Buildap was not designed to behave in this manner.

quite opposite. serialization is done via the framework - so that is why the parameters should be serilizable or primitive types. Parts should not share the same address space so passing as pointers is not an option. The question was: is serilization required - I guess from part side - and the answer is no - because serilization will be done within the framework. So if you ask me - should parameters be of serializable type - then the responce will be yes.