Whoops, looks like I spoke too soon. I had an email today: (looks like once you buy an SD card, you're stuck with that card for the life of it. No upgrade possible):
Thank you for contacting Garmin International.
Our update policy is if you purchase an eligible mapping product and you receive anything less than the most current version you can update the maps to the current version for free. You have 30 days to take advantage of that offer once your unit is purchased and the update disk is available. So no you do not get a free update for up to a year however if you by a Garmin XT product on DVD today you would be able to update it for free to 2009 if it does not have it once the update DVD is ready. Please Note that pre-programmed cards DO NOT get any kind of free update. This cards are not updateable and if you are planning on getting a pre-programmed card you will need to make sure it has 2009 on when you buy it as we will not update these cards.
With Best Regards,
Jason S, Software Support Specialist iQue Team Garmin International