1. I've been using this program for over 6 months and it's great!
2. I don't think the extended download service is worth it. This is how it works: The "retail" version of the software is only downloadable from Acronis' online distributor, which is who is selling you the extended download service, updates, however, are available indefinitely from Acronis. So, if you download the retail version after purchasing it, you can burn it to a CD and put it in a safe place. Then, as long as you have that installed on a machine, you can update it via the update downloads from Acronis. Other online software retailers use a similar scheme to tr to get your $$ (I think Symantec does it too). Much better to use a $0.50 CD than to spend more money to be able to download it in 6 months.
3. It's one license per machine, and as JohnBullard said, you do need that key included on the download screen. I think you'll find it also in the email, but it's written in extra tiny font.