Getting your Windows Phone 7 Device Syncing after upgrading to Mango on a Guest PC

During the big Mango update rush over the last 3 weeks i joined the rest of the Windows Phone 7 Development community and excitedly upgraded my phone from Windows Phone 7 Mango Beta to the real thing. I was so eager to upgrade right now that I did so on my work PC where I connect my phone as a Guest. This happily got me up and running (definite thanks to the WP7 team for doing such a great job of the upgrade experience). My troubles only began when i tried to synch my phone at home a couple of days later. Hopefully i can save a few of you the time i spent looking into this.