Our group is primarily Java developers with a few .NET folks like me.
We have a new app that we're considering and are thinking of using .NET on the front-end and Java for the app server.
What is the best way to communicate? Soap can be slow. I don't think that Serialized XML will work. I seem to recall that it is proprietary for .NET. Or will it work?
You can use JSON as format for communication. Its structured, less complicated, and lightweight.
Protocol Buffers or Hessian can provide multi-platform alternatives to SOAP. You can find some details concerning protocol buffers for .Net here.
The XML serialization is just that - XML. I can't immediately think of why there should be any issues with this idea, as long as both the .NET and Java setups are working against the same schema and objects. XML is an open format.
I think binary serialization is proprietary to .NET, and is not exchangeable with other platforms.