On the distributed computing side, there may be few surprises. J2EE employs Corba, which is an OMG specification, and enjoys several 3rd party implementations. Both frameworks support SOAP for web services. In terms of scalability, the jury is out. Both frameworks are incredibly scalable.
Scalability is definitely a fundamental design goal for both frameworks.
On balance, we feel both platforms offer excellent paradigms. We look forward to computing in both J2EE and .Net in the future.