Update: Paul Thurrott of Winsupersite.com has posted a brief article clarifying some of the things supposedly misinterpreted during this past week regarding the changes in Windows Vista licensing terms. Paul was in contact with Microsoft in order to come up with the actual meaning of their new EULA for Vista. As a starter you should know that in Vista, just like you currently do with XP, you should be able to upgrade your machine as many times as you want; only needing to re-activate your copy of the OS when prompted to, via the Internet or through the phone. This is perhaps the most important part that was being reported inaccurately. In the other hand, Paul goes as far as saying: "Microsoft has clarified the EULA for Windows Vista. They've made it more readable, for starters, so normal people can get by the legalese and understand what the document really means." I do not believe that is the case, I have read the EULA myself and for many case scenarios, the explanations Microsoft provides remain very unclear and ambiguous.
If you can't wait to rush out and buy a brand new retail copy of Vista when it hits the shelves, you may want to take a look at the new licensing that Microsoft is introducing first. "Restrictive" isn't really quite the term, accurate though it would be. "Bizarre" would fit better, and some of it is outlined here. One of the oddest things is Microsof'ts stance against virtual machines. While allowing Vista Ultimate and Business to be run in a VM, all other versions are barred from it. Meaning if you are running Basic or Premium in a VM, you're violating the license.
Vista will also strip OS functionality should validation fail. What people feared with activation in XP is now coming true in Vista. The OS will periodically "validate" itself, and if it finds that you are a dirty pirate it will limit your use. It also only allows you to transfer a license once. Meaning, if you have a Vista-equipped PC and you rebuild it, you must transfer the license... and then never again can you repeat that process. Some people are used to replacing many components of their PC quite often, going through an entire rig in mere months. Enthusiasts beware.