This is pretty straightforward. Make sure your xpage is the default launch target (Application Properties, Launch tab). On that xpage have a document data source with the default action being edit document, but compute the documentID. Have a view of your "personal" documents sorted by the user's distinguished name and to get the documentId do something like this:
var nve:NotesViewEntry = database.getView("personalsByName").getEntryByKey(context.getUser().getDistinguishedName());
return (nve == null)?null:nve.getUniversalID();
if the documentId is null, the datasource should go into createDocument mode.
Rich