As someone who uses multiple computers and has used win8 on 2 of them, I LOVE this feature! Personally I use my desktop, my netbook, my wife's computer, plus my work laptop and work desktop. Having just 2 logins (one personal, one work) across all these computers, and keeping consistent setting across all devices, would be WONDERFUL.
I set up win8 on my netbook and desktop, and this feature worked well. I set everything up on my netbook first (as it is my non mission critical machine), and later slapped in a spare drive for my desktop to try it on. When I logged in the first time the settings didnt transfer (later found out they were still downloading). After 2-3min I reset the computer after installing some software. When it came back it had my user pic, background pick, lock screen pic, transferred my login settings (Pin, password, touch password), and synced my little test folder for the new file syncing through skydrive. In theory the final version will also transfer all programs purchased on the marketplace, and some other things.
Obviously the down side is that if your liveID is compromised then it is just about the end of the world as the person could change your user password and lock you out of all of your computers at once. But practically speaking I doubt this would happen unless a specific person is targeted (or leaves their computer on in a room full of teenagers!)
All of that said, I think I am going to sit out on win8 (unless RC is amazingly good). I love win7, and as much as I like the general direction they are going with win8 (the detail and control over the system is amazing) I do not see an immediate reason to upgrade. Traditionally I have skipped every other version (with the exception of win2K to XP), and I think I will continue that trend. It is just too expensive to update the 5 home computers OS every 2-3 years, better to wait 5-6.
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