Beware of XMLSerializer Woes
Careful examination of the MSDN Documenation for XMLSerializer reveals that the XMLSerializer class dynamically generates assemblies for each type that requires serialization. These assemblies are re-used only of certain "good" constructors are utilized. Use of the other "bad" constructors will result in re-generation of these assemblies. For long running processes (ASP.NET apps for example) re-generation will result in poor performance, and memory leaks. Read the documentation well taking note of the section title "Dynamically Generated Assemblies".
See also MS Knowledgebase article here: http://support.microsoft.com/kb/886385/en-us