WCF can be quite annoying - that is, it sometimes does thing in a way I personally don't like.
While happily coding FIFI (the Fast Infoset implementation for WCF that will be demoed on JavaOne), I noticed that the System.ServiceModel.Message.Write(XmlWriter) method does not use WriteStartDocument and WriteEndDocument. This is quite annoying, since nodes in FI need to be properly terminated. Sigh ...