Scott, you might want to check into this, or maybe someone here can elaborate on their experience with Garmin/Magellan/Tom Tom ect. I don't own a GPS but several of my neighbours do...they say certain co's allow updates for a yr, then you have to pay $$ for further updates, but one of the companies(Tom Tom or Magellan?) allows lifetime updates. Don't quote me, but I think it might be worthwhile finding out about the upgradeability of each of the units and if there's costs or time limits involved.
