Weird ass bug that I'll file for 10049, but seeing if anyone else here has managed to get it.
It seems when I let Windows idle.. it'll just stop letting anything spawn new content?. Like, if I leave Skype up, Skype will stop updating with new messages, and as soon as you click in the window I'll get the spinning circle of doom. Chrome/IE/Firefox will open new tabs, but they'll all be blank, and existing tabs can no longer load new sites or go anywhere. If you try to bring up Task Manager, it'll let me do it, then when i click in the Task Manager window it'll fade out too. All network activity dies.
The Windows UI itself will still work, but as soon as you launch anything, same stuff happens.
Also, if you force shutdown out of this state, Windows doesn't even complain that it was forcibly shut down, it just boots up.