If you are talking about The sony update servie that comes with the phone (im pretty sure you are ;) ) then no, it does not work. The seus only updates a small part of the firmware, and your w580 should be up to date. I ran it and it said mine was uptodate.
oh, and if you want to mess around with flashing, use xs++ to make a backup of your factory firmware. that way, if you do mess up, you have something to go back on...
Im sure sony has worked with rogers an at&t to update the firmware and keep the branded parts there....
ps give thanks! (thanks button) :)