I read this useful article @ InfoQ (http://www.infoq.com/news/2008/03/wcf-metro-interop). Its really interesting to see how top distributed computing technologies at Sun (Metro) and Microsoft (WCF) are interoperable. On the very basic level all the web services are supposed to be interoperable on WS-I basic profile. But when it comes to more advances WS-* protocols like WS-Security, WS-Atomic Transaction, WS-Reliable Messaging etc. thats when interoperability problems come to the surface. Its a great initiative from Sun and Microsoft. For more details on the interoperability results do check out Harold Carr's blog(http://weblogs.java.net/blog/haroldcarr/archive/2008/03/metro_web_servi_2.html).