Thanks Scott! That was a very good page to bookmark. And it did include the inforrmation that slartabartfast mentioned as well. Looks like I'm all set for a future windows 8 upgrade. :)
There may well be a time limit on how long your purchase will be usable. In this article Paul Thurrott says that you must use your emailed link by October 26, 2015. He does not cite a source for that. And from the way he has written it, it is not completely clear to me what exactly will expire on that date. Most likely he seems to be saying that the link in your email will no longer work to download the installer. That would not really be a problem if you have downloaded an iso. You can install Win8 upgrade on a new computer without an internet connection from the iso burned to an installation DVD, and the DVD contains everything you need to do the installation. Apparently there is nothing machine specific on that ISO, even though you have to go through the song and dance about what will be compatible on the computer you use to download it. So you do not need to actually download the installer at a later date if you have the iso.
But if the October 2015 date, means that your license will no longer work to activate a new installation, that really would be a dead end date. MS could easily enough sort out which Product Codes were issued via the introductory offer, and invalidate any that were not entered into their activation database by that date, but that seems pretty unlikely. They have enough trouble with people who need to re-install and reactivate already, without creating an army of zombie product keys and angry customers.
http://winsupersite.com/windows-8/windows-8-tip-buy-electronic-upgrade-now-install-it-later