Well, I really do not have any big secrets to uncover, but I wanted to point you WCF developers to an extremely useful tool: sgen.exe.
In itself the tool is quite handy, since you can pre-generate and compile serialization code that would otherwise be generated and compiled by WCF during runtime. The cost for doing this (while only during startup) is quite significant, so using sgen.exe, you can avoid this penalty.
The by far best part of sgen.exe is, however, the ‘/keep’ switch. If you turn this on, WCF keeps the source code for the custom IXmlSerializable implementation, and you can tweak, adjust or – in my case – debug – your serialization process.