Despite numerous people pre-loading Left 4 Dead 2's exclusive demo, PC users appear to be left in the dark waiting for it to unlock. It was originally scheduled to unlock sometime today, October 27th, but so far we just have an "unreleased" status.
We would assume Valve is aware of the problem, there's plenty of angry forum posters everywhere, but so far they haven't responded. Thankfully Xbox 360 owners are unaffected, and many have download and are currently playing said demo. We'll update the post as soon as our status changes from "unreleased" to "impending zombie horde."
Update: It looks like Valve has officially moved the demo till 11PM Pacific - or 2AM on October 28th Eastern.
Update 2: And it's pushed back again. Official time of unlocking is today, October 28th at 1PM Eastern.