Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
That's what it turned out to be for most of us. Just don't uninstall what has already downloaded, as all of the first round will remain on your drive. Your planes will not remain, just your basic program, scenery, lessons, adventures, etc. Approximately 35-38GB of stuff. The rest downloads each time you start the sim.I'll try the reboot. More and more it feels like a server overload issue on the MS side.