While I wasn't looking, Doug Purdy, who is the PM for the team in charge of the XmlSerializer has posted this little cryptic answer to my initial question:

String serializedDateTime = XmlConvert.ToString( someDateTime );

DateTime deserializedDateTime = XmlConvert.ToDateTime( serializedDateTime );

What Doug is showing is really what the serializer is doing with dates under the hood and that I am incorrectly blaming the XmlSerializer for the lack of UTC support. [XmlConvert.ToString() also does nothing more than calling DateTime.ToString() with the appropriate format string]. As I was already saying in yesterday's post, but what I want to make a bit clearer here again is that the actual problem is the lack of time-zone awareness in DateTime.

So the proper thing more me to do is to ask the base-class library team for time-zone support in the base-class library for Whidbey so that Doug can fix this for us ;)