SPFieldText fldGuid = (SPFieldText)newList.Fields.CreateNewField(SPFieldType.Text.ToString(), Constants.FieldGuid);So here I'm creating a new Text field with the name of "GUID" and adding it to the list. This works great in the code, the list is created and my column is there. This can be easily confirmed by surfing to list and visually checking.
What?! After some head scratching I remember that SharePoint has a set of reserved names that you cannot use for your column names. GUID is definitely one of those.
You can get a complete list of the reserved names here: Reference list for SharePoint internal field names.
So, the moral of the story here is keep in mind reserved column names when programmatically creating lists and columns in SharePoint. As you can see in this example, SharePoint will not throw any errors, just modify the internal name for you!