I've not looked at whether this is a new custom field or an existing one,
but if we are worried about dates > 2038 or <1970, we should probably look
at handling date time using the DateTime object within php -
http://us3.php.net/manual/en/class.datetime.php, and storing that as a
serialized result in some form. This would then give +/- ~200billion years,
and we definitely won't need to worry about