Indeed, it can take a long time. I believe what you are seeing is the loading of the most current map - most often, by the time units get to the consumer, the map that was originally loaded is out of date, and TomTom offers a service whereby you get the most recent map one time to get you up to date after your purchase.
Yes, it can take a while. You are receiving a map for the entirety of the USA and Canada, and depending upon server load and the speed of your connection, it can take quite a long while to transfer that much information.
What sort of connection do you have there to the outside world?
Keep us posted on your progress.
Also, let us know what you think of that screen. I also have a 1605, and am amazed not just at the size, but at the quality of the image with the enhanced resolution compared to my other TomTom units.